Communication system, communication apparatus and communication method

ABSTRACT

A method for a communication device includes determining whether a first radio frequency (RF) signal at a level of at least a first predetermined field threshold is detected. The method also includes generating a second RF signal at a level of at least a second predetermined field threshold greater than the first predetermined field threshold, when the communication device receives an instruction to generate the second RF signal and the determining determines that the first RF signal at the level of at least the first predetermined field threshold is not detected. The method further includes receiving a load modulated RF signal in response to the second RF signal.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 13/614,832, filedSep. 13, 2013, which is a continuation of U.S. Ser. No. 10/538,659,filed May 3, 2006, the entire contents of which are incorporated hereinby reference. U.S. Ser. No. 10/538,659 (now U.S. Pat. No. 8,514,688) isa national stage of PCT Application No. PCT/JP2003/15646, filed Dec. 8,2003, and claims the benefit of priority under 35 U.S.C. §119 fromJapanese Patent Application JP 2002-364747, filed on Dec. 17, 2002.

TECHNICAL FIELD

The present invention relates to a communication system, a communicationdevice, and a communication method, and more particularly to, acommunication system, a communication device, and a communication methodfor easily solving a problem of a so-called hidden terminal that iscaused in the wireless communication such as near field communication.

BACKGROUND ART

As a near-field communication system, e.g., an IC (Integrated Circuit)system is widely known. In the IC card system, a reader/writer generatesan electromagnetic wave, thereby generating a so-called RF (RadioFrequency) filed (magnetic field). An IC card is close to thereader/writer, then, the power is supplied to the IC card received byelectromagnetic induction, and data is transferred between the readerand the writer.

The current specification of the IC card system includes a type A, atype B, and a type C.

The type A is used by Royal Philips Electronics as an MIFARE system. Inthe type A, data is encoded by Miller in the data transfer from thereader/writer to the IC card, and data is encoded by Manchester in thedata transfer from the IC card to the reader and the writer. Further,the type A uses, as a data transfer rate, 106 kbps (kilo bit persecond).

In the type B, data is encoded by NRZ in the data transfer from thereader/writer to the IC card, and the data is encoded by NRZ-L in thedata transfer from the IC card to the reader/writer. Further, the type Buses, as a data transfer rate, 106 kbps.

The type C is used as a FeliCa system of Sony Corporation serving as thepresent applicant. Data is encoded by Manchester in the data transferbetween the reader and the writer and the IC card. Further, the type Cuses, as a data transfer rate, 212 kbps.

In the wireless communication such as near field communication, theproblem of the so-called hidden terminal might be caused and thereforeit is important to solve the problem.

For example, in a conventional wireless LAN (Local Area Network) system,generally, commands RTS (Request to send) and CTS (Clear to send) arereceived and sent in the data communication, thereby solving the problemof the hidden terminal (e.g., in non-patent document ANSI/IEEE Std802.11, 1999 Edition, LOCAL AND METROPOLITAN AREA NETWORKS: WIRELESSLAN, Chapter 9 MAC sublayer functional description).

Here, the problem of the hidden terminal has the following problems.

That is, in the wireless communication, one of a plurality ofcommunication devices sends data to another and then it is controlledthat both the communication devices simultaneously do not output theelectric wave (electromagnetic wave). Specifically, the communicationdevice for outputting the electric wave detects the peripheral electricwave. In the case of detecting the peripheral electric wave, thecommunication device for outputting the electric wave does not outputthe electric wave. In the case of detecting no electric wave, thecommunication device for outputting the electric wave outputs theelectromagnetic wave. Thus, the electric wave is alternately outputtedbetween the one communication device and the other communication devicefor receiving and sending data.

When the communication device for outputting the electric wave controlsthe output of electric wave depending on the presence or absence ofperipheral electromagnetic wave as mentioned above, one communicationdevice might simultaneously send data to other communication devices andthen the one communication device cannot receive the data.

That is, it is assumed that three communication devices A, B, and Cexist. Then, the distance between the communication devices A and B isto control the exclusive use of electric wave therebetween. Further, thedistance between the communication devices B and C is to control theexclusive use of electric wave therebetween. However, the distancebetween the communication devices A and C is not to control theexclusive use of electric wave therebetween.

In this case, the communication device B does not output the electricwave when any of the communication device A and the communication deviceC outputs the electric wave. However, the communication device A outputsthe electric wave when the communication device C outputs the electricwave. Further, the communication device C outputs the electric wave whenthe communication device A outputs the electric wave.

When the communication devices A to C have the above-mentionedrelationships, both the communication devices A and C mightsimultaneously send the electric wave (data) to the communication deviceB. For example, the distance between the communication devices B and Ais equal to the distance between the communication devices B and C andboth the communication devices A and C output the electric wave with thesame strength, then, and the communication device B receives theindividual electric waves outputted from the communication devices A andC with the same strength. Consequently, the crosstalk does not enablethe normal reception of the data from both communication devices A andC.

As mentioned above, the communication device B does not normally receivethe data because the communication device A confirms the existence ofthe communication device B and, however, does not confirm the existenceof the communication device C, and the communication device C furtherconfirms the existence of the communication device B and, however, doesnot confirm the existence of the communication device A. As mentionedabove, the problem of the hidden terminal is that both the communicationdevices A and C are hidden from each other and are not viewed from eachother and therefore the crosstalk is caused in the communication deviceB by simultaneously outputting the electric waves from both thecommunication devices A and C.

Then, in the conventional wireless LAN, the communication device on thecommunication source for starting the communication sends the commandRTS for informing a communication time (time for sharing the space) tothe communication device serving as the communication partner. Thecommunication device, serving as the communication partner, forreceiving the command RTS returns the command CTS for informing theacceptance for the command RTS and the communication time (time forsharing the space) to the communication device on the communicationsource. Other communication devices having the distance for receivingthe command RTS or CTS from the communication device on thecommunication source or as the communication partner recognize the spacesharing in one time for sharing the space in accordance with the commandRTS or CTS, and do not send the electric wave (data) in the time forsharing the space.

In the communication devices A to C having the above-mentionedpositional relationships, the communication device A sends the commandRTS to the communication device B, and the communication device B sendsthe command CTS, serving as a response for the command RTS, to thecommunication device A. The communication device C can receive thecommand CTS sent by the communication device B and the communicationdevice C receives the command CTS sent by the communication device B andthen does not send the electric wave. Consequently, the communicationdevice B prevents the collision of electric waves (data) from thecommunication devices A and C.

However, according to the solving method of the problem of the hiddenterminal by using the commands RTS and CTS, the communication deviceneeds control logic and memory therefore and thus costs are increased.

DISCLOSURE OF INVENTION

The present invention is devised in consideration of the above-mentionedsituation to solve the problem of the hidden terminal.

According to the present invention, in a communication system, whendetecting means does not detect the electromagnetic wave at the level ofa first threshold or more, a first communication device starts to outputan electromagnetic wave and a second communication device requires theelectromagnetic wave at the level of a second threshold or more higherthan the first threshold so as to obtain data by demodulating means.

According to the present invention, when the detecting means does notdetect the electromagnetic wave at the level of the first threshold ormore, the first communication device starts to output theelectromagnetic wave, and the electromagnetic wave communicates withanother device at the position where it reaches at the level of thesecond threshold or more higher than the first threshold.

According to the present invention, in a first communication method,when a detecting step does not detect the electromagnetic wave at thelevel of the first threshold or more, an output of the electromagneticwave starts and the electromagnetic wave communicates with the otherdevice at the position where it reaches at the level of the secondthreshold or more higher than the first threshold.

According to the present invention, the second communication devicerequires the electromagnetic wave at the level of the second thresholdor more higher than the first threshold so as to obtain data bydemodulating means when the other device checks that the electromagneticwave at the level of the first threshold or more does not exist and theoutput of the electromagnetic wave starts.

According to the present invention, a second communication method needsthe electromagnetic wave at the level of the second threshold or morehigher than the first threshold so as to obtain data by demodulatingmeans when the other device checks that the electromagnetic wave at thelevel of the first threshold or more does not exist and the output ofthe electromagnetic wave starts.

According to the present invention, in the communication system, whenthe electromagnetic wave at the level of the first threshold or more isnot detected, the first communication device starts to output theelectromagnetic wave and the second communication device needs theelectromagnetic wave at the level of the second threshold or more higherthan the first threshold so as to obtain the data.

According to the present invention, in the first communication deviceand communication method, when the electromagnetic wave at the level ofthe first threshold or more is not detected, the output of theelectromagnetic wave starts and the electromagnetic wave is communicatedwith the other device at the position where it reaches at the level ofthe second threshold or more higher than the first threshold.

According to the present invention, in the second communication deviceand communication method, when the other device checks that theelectromagnetic wave at the level of the first threshold or more doesnot exist and the output of the electromagnetic wave starts, the dataacquisition needs the electromagnetic wave at the level of the secondthreshold or more higher than the first threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of the structure of acommunication system according to a first embodiment.

FIG. 2 is an explanatory diagram of a passive mode.

FIG. 3 is an explanatory diagram of an active mode.

FIG. 4 is a block diagram showing an example of the structure of an NFCcommunication device 1.

FIG. 5 is a block diagram showing one example of a demodulating unit 13.

FIG. 6 is a block diagram showing one example of a modulating unit 19.

FIG. 7 is a block diagram showing another example of the demodulatingunit 13.

FIG. 8 is a block diagram showing another example of the demodulatingunit 13.

FIG. 9 is a timing chart for explaining initial RFCA processing.

FIG. 10 is a timing chart for explaining active RFCA processing.

FIG. 11 is an explanatory diagram of SDD processing.

FIG. 12 is a diagram showing a list of commands and responses.

FIG. 13 is a flowchart for explaining processing of an NFC communicationdevice.

FIG. 14 is a flowchart showing processing of an initiator in the passivemode.

FIG. 15 is a flowchart showing target processing in the passive mode.

FIG. 16 is a flowchart showing processing of the initiator in the activemode.

FIG. 17 is a flowchart showing target processing in the active mode.

FIG. 18 is a flowchart showing communication processing of the initiatorin the passive mode.

FIG. 19 is a flowchart showing communication processing of the initiatorin the passive mode.

FIG. 20 is a flowchart showing communication processing of the target inthe passive mode.

FIG. 21 is a flowchart showing communication processing of the initiatorin the active mode.

FIG. 22 is a flowchart showing communication processing of the initiatorin the active mode.

FIG. 23 is a flowchart of communication processing of the target in theactive mode.

FIG. 24 is an explanatory diagram of one example of processing forcoping with the problem of the hidden terminal.

FIG. 25 is an explanatory diagram of another example of processing forcoping with the problem of the hidden terminal.

FIG. 26 is an explanatory diagram of another example of processing forcoping with the problem of the hidden terminal.

FIG. 27 is a flowchart showing processing for controlling the receptionand transmission of the initiator in the passive mode.

FIG. 28 is a flowchart showing processing for controlling the receptionand transmission of the target in the passive mode.

FIG. 29 is a flowchart showing processing for controlling the receptionand transmission of the initiator in the active mode.

FIG. 30 is a flowchart showing processing for controlling the receptionand transmission of the target in the active mode.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an example of the structure a communication system (here,system is formed by logically combining a plurality of devices,irrespective of whether or not the devices are arranged in the samecasing) according to an embodiment.

Referring to FIG. 1, the communication system comprises three NFCcommunication devices 1, 2, and 3. The NFC communication devices 1 to 3perform NFC (Near Field Communication) by electromagnetic inductionbetween one NFC communication device and another with carriers having asingle frequency.

The NFC communication devices 1 to 3 use a carrier frequency of, e.g.,13.56 MHz of ISM (Industrial Scientific Medical) band.

The near field communication means the communication that is establishedwithin the distance between the devices for communication of severaltens cm, including the communication of the contact devices (casings)for communication.

The communication system shown in FIG. 1 may be an IC card system, inwhich at least one of the NFC communication devices 1 to 3 is used as areader/writer and further another NFC communication device is used as anIC card. In addition, each of the NFC communication devices 1 to 3 maybe a communication system of a PDA (Personal Digital Assistant), a PC(Personal Computer), a mobile phone, a watch, or a pen. That is, the NFCcommunication devices 1 to 3 are devices for Near-Field Communication,and are not limited to the IC card in the IC card system or thereader/writer.

The NFC communication devices 1 to 3 have two features. First, the NFCcommunication devices 1 to 3 can communicate data with each other in twocommunication modes. Secondarily, the NFC communication devices 1 to 3can transfer data at a plurality of transfer rates.

The two communication modes are a passive mode and an active mode. Now,the communication between the NFC communication devices 1 and 2 isfocused from the NFC communication devices 1 to 3. Then, in the passivemode, similarly to the above-mentioned conventional IC card system, oneof the NFC communication devices 1 and 2, e.g., the NFC communicationdevice 1 modulates (the carrier corresponding to) the electromagneticwave generated by the NFC communication device 1, thereby sending thedata to the NFC communication device 2 serving as the other NFCcommunication device 2. The NFC communication device 2 modulates theload of (the carrier corresponding to) the electromagnetic wavegenerated by the NFC communication device 1, thereby sending the data tothe NFC communication device 1.

On the other hand, in the active mode, both the NFC communicationdevices 1 and 2 modulate (the carrier corresponding to) theelectromagnetic waves generated by the NFC communication devices 1 and2, thereby sending the data.

In the case of near field communication with the electromagneticinduction, an initiator denotes the device which first outputs theelectromagnetic wave to start the communication and, that is, has theinitiative for communication. In the near field communication, theinitiator sends a command to the communication partner and thecommunication partner returns a response for the command. A targetdenotes the communication partner that sends a response to the commandfrom the initiator.

For example, the NFC communication device 1 starts to output theelectromagnetic wave to start the communication with the NFCcommunication device 2. Then, referring to FIGS. 2 and 3, NFCcommunication device 1 is the initiator, and the NFC communicationdevice 2 is the target.

In the passive mode, referring to FIG. 2, the NFC communication device 1continuously outputs the electromagnetic wave. The NFC communicationdevice 1 modulates the electromagnetic wave outputted by the NFCcommunication device 1, thereby sending the data to the NFCcommunication device 2 serving as the target. The NFC communicationdevice 2 modulates the load of the electromagnetic wave outputted by theNFC communication device 1 serving as the initiator, thereby sending thedata to the NFC communication device 1.

In the active mode, referring to FIG. 3, the NFC communication device 1serving as the initiator starts to output the electromagnetic wave byitself in the case of sending the data by itself, modulates theelectromagnetic wave, thereby sending the data to the NFC communicationdevice 2 serving as the target. The NFC communication device 1 stops theoutput of the electromagnetic wave after ending to send the data. TheNFC communication device 2 serving as the target starts to output of theelectromagnetic wave by itself in the case of sending the data byitself, and modulates the electromagnetic wave, thereby sending the datato the NFC communication device 2 serving as the target. The NFCcommunication device 2 stops the output of the electromagnetic waveafter ending to send the data.

The second feature that the NFC communication devices 1 to 3 cantransfer the by the plurality of transfer rates will be described later.

Referring to FIG. 1, the three NFC communication devices 1 to 3 form thecommunication system. The number of the NFC communication devicesforming the communication system is not limited to three and may be twoor four or more. Further, the communication system may include not onlythe NFC communication device but also an IC card or a reader/writerforming the conventional IC card system.

FIG. 4 shows an example of the structure of the NFC communication device1 shown in FIG. 1. The remaining NFC communication devices 2 and 3 shownin FIG. 1 is similar to the NFC communication device 1 shown in FIG. 4and therefore a description is omitted.

An antenna 11 forms a loop coil. The current flowing to the coil changesand the antenna 11 outputs the electromagnetic wave. The magnetic fluxpassing through the coil serving as the antenna 11 changes, therebyflowing the current to the antenna 11.

The receiving unit 12 receives the current flowing to the antenna 11,tunes and detects the signal, and outputs the signal to a demodulatingunit 13. The demodulating unit 13 demodulates the signal supplied fromthe receiving unit 12, and supplies the demodulated signal to thedecoding unit 14. The decoding unit 14 decodes Manchester code suppliedfrom the demodulating unit 13, and supplies data as a decoding result tothe data processing unit 15.

The data processing unit 15 performs predetermined processing based onthe data supplied from the decoding unit 14. Further, the dataprocessing unit 15 supplies, to an encoding unit 16, the data to be sentto another device.

The encoding unit 16 encodes the data supplied from the data processingunit 15 to e.g., Manchester code, and supplies the encoding data to aselecting unit 17. The selecting unit 17 selects one of a modulatingunit 19 and a load modulation unit 20, and outputs the signal suppliedfrom the encoding unit 16 to the selected unit.

The selecting unit 17 selects a modulating unit 19 or a load modulationunit 20 under the control of a control unit 21. When the communicationmode is the passive mode and the NFC communication device 1 is thetarget, the control unit 21 allows the selecting unit 17 to select theload modulation unit 20. When the communication mode is the active modeor when the communication mode is the passive mode and the NFCcommunication device 1 is the initiator, the control unit 21 allows theselecting unit 17 to select a modulating unit 19. In the case in whichthe communication mode is the passive mode and the NFC communicationdevice 1 is the target, the signal outputted by the encoding unit 16 issupplied, via the selecting unit 17, to the load modulation unit 20. Inanother case, the signal outputted by the encoding unit 16 is supplied,via the selecting unit 17, to the modulating unit 19.

The electromagnetic-wave output unit 18 flows, from the antenna 11 tothe antenna 11, the current for irradiating (the electromagnetic wave)of the carrier with the predetermined single frequency. The modulatingunit 19 modulates the carrier, serving as the current flowed to theantenna 11 by the electromagnetic-wave output unit 18 in accordance withthe signal supplied from the selecting unit 17. Thus, antenna 11irradiates the electromagnetic wave obtained by modulating the carrierin accordance with the data outputted to the encoding unit 16 by theprocessing unit 15.

The load modulation unit 20 changes the impedance in the case ofexternally viewing in accordance with the signal supplied from theselecting unit 17. When another device outputs the electromagnetic waveas the carrier and thus the RF field (magnetic filed) is generatedaround the antenna 11, the impedance changes in the case of externallyviewing the coil as the antenna 11, thereby changing the RF field aroundthe antenna 11. Consequently, the carrier serving as the electromagneticwave outputted by the other device is modulated in accordance with thesignal supplied from the selecting unit 17. The data outputted from thedata processing unit 15 to the encoding unit 16 is sent to the otherdevice that outputs the electromagnetic wave.

The modulating system of the modulating unit 19 and the load modulationunit 20 is e.g., ASK (Amplitude Shift Keying). However, the modulatingsystem of the modulating unit 19 and the load modulation unit 20 is notlimited to ASK, and may use other modulating systems such as PSK (PhaseShift Keying) and QAM (Quadrature Amplitude Modulation). Further, thedegree of modulation is not limited to 8%, 30%, 50%, and 100% and maypreferably be selected.

The control unit 21 controls the blocks forming the NFC communicationdevice 1. The power supply unit 22 supplies necessary power to theblocks forming the NFC communication device 1. Referring to FIG. 4, thedrawing for controlling the blocks forming the NFC communication device1 by the control unit 21 and the drawing for supplying the power to theblocks forming the NFC communication device 1 by the power supply unit22 are complicated and therefore they are omitted.

Similarly to the receiving unit 12, the detecting unit 23 receives thecurrent flowing into the antenna 11, and detects based on the currentwhether or not the antenna 11 receives the electromagnetic wave at apredetermined threshold level (density of magnetic flux) supplied fromthe threshold setting unit 24.

The threshold setting unit 24 sets a threshold of the electromagneticlevel detected by the detecting unit 23, and the set threshold to thedetecting unit 23. The threshold setting unit 24 sets two thresholds(magnetic-flux density TH1 for determining the suppression of output ofa carrier and a magnetic-flux density TH2 of a carrier at operatinglimit, which will be described later). The detecting unit 23 detects theelectromagnetic waves at a threshold level by the threshold setting unit24 or more from the two sets thresholds. As shown by a dotted line inFIG. 4, the NFC communication device 1 has the detecting unit 25 inaddition to the detecting unit 23. The detecting unit 23 detects theelectromagnetic wave having one of the two thresholds or more. Thedetecting unit 25 detects the electromagnetic wave having the otherthreshold or more.

In this case, the decoding unit 14 and the encoding unit 16 process theManchester code of the type C. The decoding unit 14 and the encodingunit 16 selects one of a plurality of types including modified-mirrormode in the type A or NZR in the type C in addition to the Manchestercode, and processes the selected code.

FIG. 5 shows an example of the structure of the demodulating unit 13shown in FIG. 4.

Referring to FIG. 5, the demodulating unit 13 demodulates a selectingportion 31, N≧2) demodulating portions 32 ₁ to 32 _(N), and a selectingportion 33.

Under the control operation of the control unit 21 (shown in FIG. 4),the selecting portion 31 selects one of the demodulating portions 32_(n) (n=1, 2, . . . , N) from N demodulating portions 32 ₁ to 32 _(N),and supplies a signal outputted by the receiving unit 12 to the selecteddemodulating portion 32 _(n).

The demodulating portion 32 _(n) demodulates the signal sent by an n-thtransfer rate, and supplies the demodulated signal to the selectingportion 33. The demodulating portion 32 _(n) and the demodulatingportion 32 _(n′) (n≠n′) demodulate the signals sent by differenttransfer rates. Therefore, the demodulating unit 13 shown in FIG. 5demodulates the signals sent by N (first to N-th) transfer rates. The Ntransfer rates include fast 424 kbps and 848 kbps, in addition to theabove-mentioned 106 kbps and 212 kbps. That is, the N transfer ratesincludes, e.g., the existing transfer rates in the near fieldcommunication of the existing IC card system and the like.

Under the control operation of the control unit 21, the selectingportion 33 selects one demodulating portion 32 _(n) of the Ndemodulating portions 32 ₁ to 32 _(N), and supplies the demodulatedoutput obtained by the demodulating portion 32 _(n) to the decoding unit14.

With the demodulating unit 13 having the above structure, the controlunit 21 (shown in FIG. 4) allows the selecting portion 31 tosequentially select N demodulating portions 32 ₁ o 32 _(N). Thus, thedemodulating portions 32 ₁ to 32 _(N) demodulate the signals suppliedvia the selecting portion 31 from the receiving unit 12. The controlunit 21 recognizes the demodulating portion 32 _(n) that normallydemodulates the signal supplied via the selecting portion 31 from thereceiving unit 12, and controls the selecting portion 33 so as to selectthe output of the demodulating portion 32 _(n). Under the controloperation of the control unit 21, the selecting portion 33 selects thedemodulating portion 32 _(n). Thus, the output that is normallydemodulated by the demodulating portion 32 _(n) is supplied to thedecoding unit 14.

The demodulating unit 13 demodulates the signal sent by an arbitrarytransfer rate of the N transfer rates.

Only in the case of normal demodulation, the demodulating portions 32 ₁to 32 _(N) output a demodulating result. In the abnormal demodulation,no data (e.g., high impedance) is outputted. In this case, the selectingportion 33 may sets the OR operation of all outputs of the demodulatingportions 32 ₁ to 32 _(N) and may output the OR operation to the decodingunit 14.

FIG. 6 shows an example of the structure of the modulating unit 19 shownin FIG. 4.

Referring to FIG. 6, the modulating unit 19 comprises a selectingportion 41, N 2) modulating portions 42 ₁ to 42 _(N), and a selectingportion 43.

Under the control operation of the control unit 21 (FIG. 4), theselecting portion 41 selects one modulating portion 42 _(n) (n=1, 2, . .. , N) from N modulating portions 42 ₁ to 42 _(N), and supplies thesignal outputted by the selecting unit 17 (FIG. 4) to the selectedmodulating portion 42 _(n).

The modulating portion 42 _(n) modulates the carrier as the currentflowing into the antenna 11 via the selecting portion 43 in accordancewith the signal supplied from the selecting portion 41 so as to send thedata by the n-th transfer rate. The modulating portion 42 _(n) and themodulating portion 42 _(n′) (n≠n′) modulate the carrier by differenttransfer rates. Referring to FIG. 6, the modulating unit 19 sends thedata by N (first to N-th) transfer rates. The N transfer rates may bethe same transfer rate as that of the demodulation of the demodulatingunit 13 shown in FIG. 5.

Under the control operation of the control unit 21, the selectingportion 43 selects the same modulating portion 42 _(n) as that selectedby the selecting portion 41 from the N modulating portions 42 ₁ to 42_(N), and electrically connects the modulating portion 42 _(n) and theantenna 11.

For the modulating unit 19 with the above structure, the control unit 21(shown in FIG. 4) allows the selecting portion 41 to sequentially selectN modulating portions 42 ₁ to 42 _(N). Thus, the control 21 furtherallows the modulating portions 42 ₁ to 42 _(N) to modulate the carrieras the current flowing into the antenna 11 via the selecting portion 43in accordance with the signal supplied from the selecting portion 41.

The modulating unit 19 modulates the carrier and sends the data so as tosend the data by an arbitrary transfer rate of the N transfer rates.

The load modulation unit 20 shown in FIG. 4 has the same structure asthat of the modulating unit 19 shown in FIG. 6 and therefore adescription thereof is omitted.

As mentioned above, the NFC communication devices 1 to 3 modulate thecarrier to the signal of the data sent by any of the N transfer rates,and further demodulate the signal of the data sent by any of the Ntransfer rates. The N transfer rate the transfer rate that has alreadybeen used in the near field communication of the existing IC card system(FeliCa system) and another transfer rate. Among the NFC communicationdevices 1 to 3, the data is received/sent by any of the N transferrates. Further, among the NFC communication devices 1 to 3, the data isreceived/sent between the IC card and the reader/writer forming theexisting IC card system by the transfer rate used by the IC card and thereader/writer.

As a consequence, the NFC communication devices 1 to 3 are easilyapplied to services using the existing near field communication withoutuser's confusion. Further, the NFC communication devices 1 to 3 areeasily applied to services using the near field communication with thefast data rate which will be put into the market in the future togetherwith the existing the near field communication.

Among the NFC communication devices 1 to 3, the data is directlyreceived/sent, not via another device such as a reader/writer becausethe data is transferred both in the passive mode in the conventionalnear field communication and in the active mode for sending the data byoutputting the electromagnetic wave by itself.

FIG. 7 shows another example of the demodulating unit 13 shown in FIG.4. The same reference numerals denote the corresponding portions in FIG.5 and a description thereof is properly omitted. That is, basically, thedemodulating unit 13 shown in FIG. 7 has the same structure as that FIG.5, except for the selecting portion 31.

According to the embodiment, referring to FIG. 7, the signal outputtedby the receiving unit 12 is simultaneously supplied to the demodulatingportions 32 ₁ to 32 _(N). The demodulating portions 32 ₁ to 32 _(N)simultaneously demodulate the signal from the receiving unit 12. Thecontrol unit 21 recognizes the demodulating portion 32 _(n) whichnormally demodulates the signal from the receiving unit 12, and controlsthe selecting portion 33 to output the signal from the demodulatingportion 32 _(n). Under the control operation of the control unit 21, theselecting portion 33 selects the demodulating portion 32 _(n), therebysupplying the output normally demodulating the demodulating portion 32_(n) to the decoding unit 14.

Incidentally, according to the embodiment, referring to FIG. 7, thedemodulating portions 32 ₁ to 32 _(N) must always demodulate the signal.On the contrary, according to the embodiment, referring to FIG. 5, onlydemodulating devices of the demodulating portions 32 ₁ to 32 _(N) thatare selected by the selecting portion 31 demodulates the signal andanother operation stops. In view of saving the power consumption ofdevice, the structure shown in FIG. 5 is more advantageous than thatshown in FIG. 7. On the other hand, in view of early obtaining thenormal demodulated output, the structure shown in FIG. 7 is moreadvantageous than that shown in FIG. 5.

FIG. 8 shows another example of the structure of the demodulating unit13 shown in FIG. 4.

Referring to FIG. 8, the demodulating unit 13 comprises a variable-ratedemodulating portion 51 and a rate detecting portion 52.

The variable-rate demodulating portion 51 demodulates the signalsupplied from the receiving unit 12 as a signal of the transfer rate inaccordance with an instruction from the rate detecting portion 52, andsupplies the demodulating result to the decoding unit 14. The ratedetecting portion 52 detects the transfer rate of the signal suppliedfrom the receiving unit 12 and sends an instruction for demodulating thesignal of the transfer rate to the variable-rate demodulating portion51.

The demodulating portion 51 with the above structure supplies the signaloutputted by the receiving unit 12 to the variable-rate demodulatingportion 51 and the rate detecting portion 52. The rate detecting portion52 detects which one of the N (first to N-th) transfer rates is thetransfer rate of the signal supplied from the receiving unit 12, andsends an instruction for demodulating the signal of the transfer rate tothe variable-rate demodulating portion 51. The variable-ratedemodulating portion 51 demodulates the signal supplied from thereceiving unit 12 as the signal of the transfer rate in accordance withthe instruction from the rate detecting portion 52, and supplies thedemodulating result to the decoding unit 14.

Any of the NFC communication devices 1 to 3 can become the initiatorthat first outputs the electromagnetic wave and starts thecommunication. Further, in the active mode, when any of the NFCcommunication devices 1 to 3 becomes the initiator or the target, itoutputs the electromagnetic wave by itself.

When the NFC communication devices 1 to 3 are close thereto and at leasttwo of the NFC communication devices 1 to 3 simultaneously output theelectromagnetic wave, the collision is caused and the communication isnot performed.

The NFC communication devices 1 to 3 detect whether or not (the RF fieldof) the electromagnetic wave from another device exists. Only when theRF field of the electromagnetic wave from the other device does notexist, the output of electromagnetic wave starts to prevent thecollision. As mentioned above, to prevent the collision, the processingfor detecting whether or not the electromagnetic wave from anotherdevice exists and starting the output of electromagnetic wave isreferred to as RFCA (RF Collision Avoidance) processing.

The RFCA processing includes two processing of initial RFCA processingthat is first performed by the NFC communication device (at least one ofthe NFC communication device 1 to 3 in FIG. 1) serving as the initiatorand response RFCA processing that is performed by the NFC communicationdevice for starting the output of electromagnetic wave at each timingfor starting the output of electromagnetic wave in the communication inthe active mode. Both in the initial RFCA processing and the responseRFCA processing, similarly, it is detected whether or not theelectromagnetic wave from another device exists before starting theoutput of electromagnetic wave and the output of electromagnetic wavestarts only when the electromagnetic wave from the other device does notexist. However, the time from the timing for detecting no existence ofthe electromagnetic wave from the other device to the timing forstarting the output of the electromagnetic wave varies between theinitial RFCA processing and the response RFCA processing.

First, the initial RFCA processing will be described with reference toFIG. 9.

FIG. 9 shows the electromagnetic wave that starts to be outputted by theinitial RFCA. Referring to FIG. 9, (similarly, FIG. 10 which will bedescribed later), the abscissa denotes the time and the ordinate denotesthe level of the electromagnetic wave outputted by the NFC communicationdevice.

The NFC communication device serving as the initiator continuouslydetects the electromagnetic wave from another device, starts the outputof electromagnetic wave from the other device when the electromagneticwave from the other device is not continuously detected for a time(T_(IDT)+n×T_(RFW)), and starts Send Request of data (including acommand) after the passage of only time T_(IRFG) from the output timing.

Here, the time T_(IDT) of the time (T_(IDT)+n×T_(RFW)) is referred to asan initial delay time. A frequency of the carrier is designated byreference symbol f_(c) and then the time T_(IDT) as the initial delaytime is larger than 4096/f_(c) and, for example, is an integer that isnot less than 0 and not more than 3 and is generated by random numbers.The time T_(RFW) is referred to as an RF waiting time and, for example,is 512/f_(c). The time T_(IRFG) is referred to as an initial guard timeand, for example, is larger than 5 ms.

By using a random number n for the time (T_(IDT)+n×T_(RFW)) for whichthe electromagnetic wave must not be detected, the possibility forstarting the output of electromagnetic wave by a plurality of NFCcommunication devices at the same timing is suppressed.

When the NFC communication device starts to output the electromagneticwave in the initial RFCA processing, the NFC communication devicebecomes the initiator. In this case, the active mode is set as acommunication mode and then the NFC communication device as theinitiator ends the transmission of the data thereof and thereafter stopsthe output of electromagnetic wave. On the other hand, the passive modeis set as a communication mode and then the NFC communication device asthe initiator continues to output the electromagnetic wave starting bythe initial RFCA processing until the communication with the targetcompletely ends.

FIG. 10 shows the electromagnetic wave that start to be outputted by theresponse RFCA.

In the active mode, the NFC communication device for outputting theelectromagnetic wave detects the electromagnetic wave from anotherdevice. When the NFC communication device does not detect the continuousoutput of the electromagnetic wave from the other device only for thetime (T_(ADT)+n×T_(RFW)), the output of electromagnetic wave starts andSend Response of the data starts after the passage of only the timeT_(ARFG) from the output timing.

Here, reference symbols n and T_(RFW) in the time (T_(ADT)+n×T_(RFW))are as the same in the initial RFCA processing shown in FIG. 9.Reference symbol T_(ADT) in the time (T_(ADT)+n×T_(RFW)) is referred toas an active delay time that is, e.g., 768/f_(c) or more and 2559/f_(c)or less. The time T_(ARFG) is referred to as an active guard time thatis, e.g., longer than 1024/f_(c).

As will be obviously understood with reference to FIGS. 9 and 10, inorder to start the output of electromagnetic wave by the initial RFCAprocessing, the electromagnetic wave must exist for at least the initialdelay time T_(IDT). In order to start the output of electromagnetic waveby the response RFCA processing, the electromagnetic wave must not existfor at least the active delay time T_(ADT).

The initial delay time T_(IDT) is longer than 4096/f_(c). On the otherhand, the active delay time T_(ADT) is 768/f_(c) or more and is2559/f_(c) or less. Thus, when the NFC communication device becomes theinitiator, a longer time for which the electromagnetic wave does notexist is necessary, as compared with the case in which theelectromagnetic wave is outputted during the communication in the activemode. Inversely, when the NFC communication device outputs theelectromagnetic wave during the communication in the active mode, theNFC communication device must output the electromagnetic wave after notso long time from the timing at which the electromagnetic wave does notexist, as compared with the case in which the NFC communication devicebecomes the initiator. This is because of the following reasons.

That is, one NFC communication device communicates the data in theactive mode, then, another NFC communication device outputs theelectromagnetic wave by itself and sends the data and thereafter stopsthe output of electromagnetic wave. The other NFC communication devicestarts to output the electromagnetic wave and sends the data. Therefore,in the communication in the active mode, all the NFC communicationdevices might stop the output of electromagnetic wave. When the NFCcommunication device becomes the initiator, it is necessary to checkwhether or not another device does not output the electromagnetic wavearound the NFC communication device which becomes the initiator for asufficient time so as to check that the data is not communicated aroundthe NFC communication device in the active mode.

On the other hand, in the active mode, the initiator outputs theelectromagnetic wave, thereby sending the data to the target. Theinitiator stops the output of electromagnetic wave and then starts theoutput of electromagnetic wave. Thus, the target sends the data to theinitiator. After that, the target stops the output of electromagneticwave and then the initiator starts to output the electromagnetic wave,thereby sending the data to the initiator. Then, similarly, the data isreceived/sent between the initiator and the target.

When the NFC communication device exists serving as the initiator aroundthe initiator and the target in the communication in the active mode,then, one of the initiator and the target stops the output of theelectromagnetic wave in the communication in the active mode, and ittakes a long time until the other starts to output the electromagneticwave, the electromagnetic wave does not exist during the long time.Thus, the NFC communication device serving as the initiator starts tooutput the electromagnetic wave by the initial RFCA. In this case, thecommunication in the active mode that has already been executed isprevented.

Therefore, the electromagnetic wave needs to be outputted in theresponse RFCA processing in the communication in the active mode for anot so long time after the electromagnetic wave does not exist.

As mentioned with reference to FIG. 9, the NFC communication deviceserving as the initiator start to output the electromagnetic wave by theinitial and then sends the data. The NFC communication device serving asthe initiator starts to output the electromagnetic wave, therebybecoming the initiator. The NFC communication device existing near theinitiator becomes the target. In order to receive and send the datafrom/to the target of the initiator, the target for receiving andsending the data needs to be specified. Therefore, after the initiatorstarts to output the electromagnetic wave by the initial RFCA, theinitiator requests an NFCID (NFC Identification) serving as informationfor specifying the target to at least one target existing near theinitiator. The target existing near the initiator sends the NFCID forspecifying the target itself to the initiator in response to the requestfrom the initiator.

The initiator specifies the target in accordance with the NFCID sentfrom the target as mentioned above, and receives and sends the datafrom/to the specified target. Here, SDD (Single Device Detection)denotes processing in which the initiator specifies the target around(near) the initiator in accordance with the NFCID.

In the SDD processing, the initiator requests the NFCID of the target bysending a polling request frame by the initiator. The target receivesthe polling request frame, then, determines the NFCID thereof by therandom number, and sends a polling response frame having the arrangementof the NFCID. The initiator receives the polling response frame sent bythe target, thereby recognizing the NFCID of the target.

When the initiator requests the NFCID of the target therenear and aplurality of targets exist near the initiator, at least two of theplurality of targets might simultaneously send the NFCIDs. In this case,the NFCIDs sent from the at least two targets might come into collisionwith each other and the initiator cannot recognize the NFCIDs which comeinto collision.

Then, the SDD processing is performed by a method using time slot so asto prevent the collision of NFCIDs with each other as much as possible.

FIG. 11 shows the sequence of SDD processing performed by the time slot.Referring to FIG. 11, five targets #1, #2, #3, #4, and #5 exist near theinitiator.

In the SDD processing, the initiator sends the polling request frame.After ending the transmission, only for a predetermined time T_(d), thetime slot for a predetermined time T_(s) is provided. The time T_(d) is,e.g., 512×64/f_(c). The time T_(s) serving as the time slot is256×64/f_(c). Further, the time slot is specified by numberingsequential integers from zero to time slots starting from the early one.

Here, four time slots #0, #1, #2, and #3 are shown in FIG. 11. However,the number of time slots may be up to 16. The initiator designates anumber TSN of time slots arranged to one polling request frame. Thenumber TSN is included in the polling request frame and then is sent tothe target.

The target receives the polling request frame sent from the initiator,and recognizes the number TSN of time slots arranged to the pollingrequest frame. Further, the target generates an integer R within a rangeof not less than 0 to not more than (TSN-1) by the random number. At atiming of a time slot #R specified by the integer R, the target sendsthe polling request frame having the NFCID of the target.

As mentioned above, the target determines, by the random number, thetime slot serving as the timing for sending the polling response frame.Thus, the timing for sending the polling response frames by a pluralityof targets varies, thereby preventing the collision between the pollingresponse frames sent by the plurality of targets.

Incidentally, if the target determines the time slot serving as thetiming for sending the polling response frame by using the randomnumber, the time slots for sending the polling response frames by theplurality of targets match each other. Thus, the collision of thepolling response frames might be caused. According to the embodiment,referring to FIG. 11, the polling response frame of the target #4 issent at the time slot #0, the polling response frames of the targets #1and #3 are sent at the time slot #1, the polling response frame of thetarget #5 is sent at the time slot #2, and the polling response frame ofthe target #2 is sent at the time slot #3. The polling response framesof the targets #1 and #3 come into collision therewith.

In this case, the initiator does not normally receive the pollingresponse frames of the targets #1 and #3 which come into collisiontherewith. Therefore, the initiator resends the polling request frame,thereby requesting the transmission of the polling response frameshaving the NFCIDs of the targets #1 and #3 thereto. Until the initiatorrecognizes all the NFCIDs of the targets #1 to #5 therenear, thetransmission of the polling request frame by the initiator and thetransmission of the polling response frame by the target are repeated.

When the initiator resends the polling request frame and then all thetargets #1 to #5 return the polling response frames, the pollingresponse frames might come into collision therewith again. When thetarget receives the polling request frame again after not so long timefrom the receiving time of the polling request frame from the initiator,the polling request is ignored. In this case, according to theembodiment, with reference to FIG. 11, the initiator does not recognizethe NFCIDs of the targets #1 and #3 which come into collision of thepolling response for the first-sent polling request frames with eachother and therefore data is neither received nor transmitted between thetargets #1 and #3.

Then, the targets #2, #4, and #5 whose polling response frames arenormally received and whose NFCIDs are recognized by the initiator aretemporarily excluded from the communication targets, as will bedescribed later. Thus, the polling response frames serving as responsesfor the polling request frames are not returned. In this case, only thetargets #1 and #3 whose NFCIDs are not recognized by the firsttransmission of the polling request frame return the polling responseframes in response to the polling request frames which are resent by theinitiator. Therefore, in this case, the NFCIDs of all the targets #1 to#5 are recognized while suppressing the possibility of the collision ofthe polling response frames.

As mentioned above, the target receives the polling request frame andthen determines (generates) the NFCID thereof by the random number.Therefore, the same NFCIDs from different targets might be arranged tothe polling response frame and might be sent to the initiator. When theinitiator receives the polling response frame having the same NFCID atdifferent time slots, the polling request frame is resent to theinitiator, similarly to the collision of the polling response frames.

As mentioned above, the NFC communication device receives and sends thedata to/from the IC card or the reader/writer forming the existing ICcard system by the transfer rate used by the IC card and thereader/writer. When the target is the IC card of the existing IC cardsystem, the SDD processing is performed as follows.

That is, the initiator starts to output the electromagnetic wave by theinitial RFCA processing. The IC card serving as the target gets thepower from the electromagnetic wave, thereby starting the processing.Now, the target is the IC card of the existing IC card system andtherefore the operating power is generated from the electromagnetic waveoutputted by the initiator.

The target gets the power and then enters the operating state. Afterthat, the target prepares for the reception of the polling request framewithin, the longest time, 2 sec, and waits for the transmission of thepolling request frame from the initiator.

On the other hand, the initiator sends the polling request frame,irrespective of whether or not the preparation for the reception of thepolling request frame in the target ends.

When the target receives the polling request frame from the initiator,as mentioned above, the target sends the polling response frame to theinitiator at a predetermined time slot. When the initiator normallyreceives the polling response frame from the target, as mentioned above,the initiator recognizes the NFCID of the target. On the other hand,when the initiator normally does not receive the polling response framefrom the target, the initiator resends the polling request frame.

In this case, the target is the IC card of the existing IC card systemand therefore, the operating power is generated from the electromagneticwave outputted from the initiator. Thus, the initiator continues tooutput the electromagnetic wave started by the initial RFCA processinguntil the communication with the target completely ends.

Next, the NFC communication device sends the initiator sends the commandto the target, and the target sends (returns) the response for thecommand from the initiator, thereby communication data.

FIG. 12 shows the command sent to the target by the initiator and theresponse sent to the initiator by the target.

Referring to FIG. 12, the command is designated by describing charactersREQ after an under bar (_), and the response is designated by describingcharacters RES after the under bar (_). According to the embodiment,with reference to FIG. 12, the type of commands includes six ones ofATR_REQ, WUP_REQ, PSL_REQ, DEP_REQ, DSL_REQ, and RLS_REQ. Similarly tothe commands, the type of responses for the command includes six ones ofATR_RES, WUP_RES, PSL_RES, DEP_RES, DSL_RES, and RLS_RES. As mentionedabove, the initiator sends the command (request) to the target, and thetarget sends the response corresponding to the command to the initiator.The command is sent by the initiator, and the response is sent by thetarget.

The ATR_REQ command indicates that the initiator sends a notificationindicating the property (specification) to the target and requests theproperty of the target to the target. The property of the initiator ortarget includes the transfer rate of the data sent or received by theinitiator or the target. Further, the command ATR_REQ includes not onlythe property of the initiator but also the NFCID for specifying theinitiator, and the target receives the command ATR_REQ, therebyrecognizing the property and the NFCID of the initiator.

The response ATR_RES is sent to the initiator as the response for thecommand ATR_REQ when the target receives the command ATR_REQ. Theresponse ATR_RES has the property and the NFCID of the target.

Further, the information on the transfer rate as the property arrangedto the command ATR_REQ or the response ATR_RES includes all the transferrates of the data sent and received by the initiator and the target. Inthis case, the reception and transmission of the command ATR_REQ and theresponse ATR_RES are performed once between the initiator and thetarget, and thus the initiator recognizes the transfer rate forreceiving and sending the data by the target and the target recognizesthe transfer rate for receiving and sending the data by the initiator.

The command WUP_REQ is sent when the initiator selects the target forcommunication. That is, the command DSL_REQ, which will be describedlater, is sent from the initiator to the target, thereby setting thetarget to a deselecting state (state for prohibiting the transmission(response) of the data to the initiator. The command WUP_REQ is sentupon resetting the deselecting state and sending the target to a statefor sending the data to the initiator. The command WUP_REQ has the NFCIDof the target, which resets the deselecting state. From among thetargets which receive the command WUP_REQ, the target specified by theNFCID arranged to the command WUP_REQ resets the deselecting state.

The response WUP_RES is sent as the response for the command WUP_REQwhen the target specified by the NFCID arranged to the WUP_REQ resetsthe deselecting state from among the targets which receive the commandWUP_REQ.

The command PSL_REQ is sent when the initiator changes a communicationparameter on the communication with the target. Here, the communicationparameter includes the transfer rate of the data received and sentbetween the initiator and the target.

The command PSL_REQ has a value of the communication parameter after thechange, and is sent from the initiator to the target. The targetreceives the command PSL_REQ, and changes the communication parameter inaccordance with the value of the communication parameter arrangedthereto. Further, the target sends the response PSL_RES for the commandPSL_REQ.

The command DEP_REQ is sent when the initiator receives and sends(exchanges) the data (so-called real data) (with the target), and hasthe data to be sent to the target. The response DEP_RES is sent, as theresponse for the command DEP_REQ, by the target, and has the data to besent to the initiator. Therefore, by the command DEP_REQ, the data issent from the initiator to the target. By the response DEP_RES for thecommand DEP_REQ, the data is sent from the target to the initiator.

The command DSL_REQ is sent when the initiator sets the target to thedeselecting state. The target that receives the command DSL_REQ sendsthe response DSL_RES for the command DSL_REQ, thereby being set to thedeselecting state. After that, the target does not respond to thecommand other than the command WUP_REQ (that is, does not return theresponse).

The command RLS_REQ is sent when the initiator completely ends thecommunication with the target. The target that receives the commandRLS_REQ sends the response RLS_RES for the command RLS_REQ, therebycompletely ending the communication with the initiator.

Commonly, the commands DSL_REQ and RLS_REQ reset the target from thecommunication target with the initiator. However, the target reset bythe command DSL_REQ becomes a communicable state with the initiator bythe command WUP_REQ again. The target reset by the command RLS_REQ doesnot become the communicable state with the initiator only by receivingand sending the above-mentioned polling request frame and pollingresponse frame to/from the initiator. The commands DSL_REQ and RLS_REQare different in the above point.

The reception and transmission of the command and the response areexecuted on, e.g., a transport layer.

Next, a description is given of communication processing of the NFCcommunication device with reference to a flowchart of FIG. 13.

Starting the communication, in step S1, the NFC communication devicedetermines whether or not the electromagnetic wave of another device isdetected.

In the NFC communication device (shown in FIG. 4), the control unit 21monitors the detecting result of the electromagnetic wave(electromagnetic wave that is similar to the electromagnetic wave andthat has the similar frequency band used by the NFC communicationdevice) of the detecting unit 23. In step S1, it is determined based onthe detecting result whether or not the electromagnetic wave of theother device is detected. In this case, the threshold setting unit 24shown in FIG. 4 sets, as a threshold, a magnetic-flux density TH1 fordetermining the suppression of output of a carrier, which will bedescribed later with reference to FIGS. 24 to 26, and supplies thethreshold to the detecting unit 23. Further, the detecting unit 23detects the level of the magnetic-flux density TH1 or more fordetermining the suppression of the output of carrier, as the thresholdsupplied from the threshold setting unit 24.

When it is determined in step S1 that the electromagnetic wave of theother device is not detected, the processing sequence advances to stepS2 whereupon the NFC communication device sets the communication mode tothe passive mode or the active mode and performs the processing of theinitiator in the passive mode or the processing of the initiator in theactive mode, which will be described later. The NFC communication devicereturns to step S1 after ending the processing and, after that, repeatsthe similar processing.

In step S2, the communication mode of the NFC communication device maybe the passive mode and the active mode, as mentioned above. Only whenthe target becomes the target in the passive mode of the IC card in theexisting IC card system, in step S2, the NFC communication device needsto set the communication mode as the passive mode, and to perform theprocessing of initiator in the passive mode.

When it is determined in step S1 that the electromagnetic wave of theother device is detected, that is, the electromagnetic wave of the otherdevice is detected near the NFC communication device, the processingsequence advances to step S3 whereupon the NFC communication devicedetermines whether or not the electromagnetic wave detected in step S1is continuously detected.

When it is determined in step S3 that the electromagnetic wave iscontinuously detected, the processing sequence advances to step S4whereupon the NFC communication device sets the communication mode asthe passive mode and performs the target processing in the passive mode,which will be described later. That is, when the electromagnetic wave iscontinuously detected, another device near the NFC communication devicebecomes the initiator in the passive mode, thereby continuouslyoutputting the electromagnetic wave started by the initial RFCAprocessing. The NFC communication device becomes the target in thepassive mode, and performs the processing. After ending the processing,the processing returns to step S1 and then the similar processing isrepeated.

Further, when it is determined in step S3 that the electromagnetic waveis not continuously detected, the processing sequence advances to stepS5 whereupon the NFC communication device sets the communication mode asthe active mode and executes the target processing in the active mode,which will be described later. That is, when the electromagnetic wave isnot continuously detected, the other device near the NFC communicationdevice becomes the initiator in the active mode and starts to output theelectromagnetic wave by the initial RFCA processing. After that, theoutput of electromagnetic wave stops. Thus, the NFC communication devicebecomes the target in the active mode. After ending the processing, theprocessing returns to step S1 and then the similar processing isrepeated.

Next, a description is given of the processing of the initiator in thepassive mode by the NFC communication device with reference to aflowchart of FIG. 14.

In the processing of the initiator in the passive mode, in step S11, theNFC communication device starts to output the electromagnetic wave. StepS11 in the processing of the initiator in the passive mode is executedwhen the electromagnetic wave is not detected in step S1 in FIG. 13 asmentioned above. That is, when the electromagnetic wave is not detectedin step S1 in FIG. 13, in step S11, the NFC communication device startsto output the electromagnetic wave. Therefore, the processing in stepsS1 and S11 corresponds to the above-mentioned initial RFCA processing.

In step S12, the NFC communication device sets a variable n indicatingthe transfer rate as an initial value and then the processing sequenceadvances to step S13. In step S13, the NFC communication device sendsthe polling request frame by an n-th transfer rate (hereinafter,referred to as an n-th rate if necessary) and then the processingsequence advances to step S14. In step S14, the NFC communication devicedetermines whether or not the other device sends the polling responseframe by the n-th rate.

When it is determined in step S14 that the other device does not sendthe polling response frame, that is, the other device near the NFCcommunication device does not communicate the data by the n-th rate andthe polling response frame for the polling request frame sent by then-th rate is not returned, steps S15 to S17 are skipped and then theprocessing sequence advances to step S18.

When it is determined in step S14 that the other device sends thepolling response frame by the n-th rate, that is, the other device nearthe NFC communication device communicates the data by the n-th rate andthe polling response frame for the polling request frame sent by then-th rate is returned, the processing sequence advances to step S15whereupon the NFC communication device sets the other device thatreturns the polling response frame as the target in the passive mode,the NFCID of the target is recognized by the NFCID arranged to thepolling response frame, and it is recognized that the target iscommunicable by the n-th rate.

In step S15, the NFC communication device recognizes the NFCID of thetarget in the passive mode and that the target is communicable by then-th rate. Then, the transfer rate to the target is (temporarily)determined as the n-th rate. As long as the command PSL_REQ does notchange the transfer rate, the communication with the target is performedby the n-th rate.

After that, in step S16, the NFC communication device sends, by the n-thrate, the command DSL_REQ to the target of the NFCID recognized in stepS15 (the target in the passive mode). Thus, the target is set to thedeselecting state so as to prevent the responding operation to the sentpolling request frame and the processing sequence advances to step S17.

In step S17, the NFC communication device receives the response DSL_RESreturned by the target in the deselecting state set by the commandDSL_REQ sent in step S16, and then the processing sequence advances tostep S18.

In step S18, the NFC communication device sends the polling requestframe by the n-th rate in step S13 and then determines whether or not apredetermined time passes. The predetermined time in step S18 is zero ormore.

When the polling request frame in step S13 is sent by the n-th rate andthe predetermined does not pass in step S18, the processing sequencereturns to step S13 and the processing in steps S13 to S18 is repeated.

By repeating the processing in steps S13 to S18, the NFC communicationdevice receives the polling response frame sent at the timing of thedifferent time slot as mentioned above with reference to FIG. 11.

When the polling request frame in step S13 is sent by the n-th rate andthen the predetermined time passes in step S18, the processing sequenceadvances to step S19 whereupon the NFC communication device determineswhether or not a variable n is equal to the value N serving as themaximum value. When it is determined in step S19 that the variable n isnot equal to the maximum value N, that is, when the variable n is lessthan the maximum value N, the processing sequence advances to step S20whereupon the NFC communication device increments the variable n by one.Then, the processing sequence returns to step S13 and the processing insteps S13 to S20 is repeated.

By repeating the processing in steps S13 to S20, the NFC communicationdevice sends the polling request frame by N transfer rates, and receivesthe polling response frames returned by the transfer rates.

When it is determined in step S19 that the variable n is equal to themaximum value N, that is, the NFC communication device sends the pollingrequest frame by N N transfer rates and the polling response framesreturned by the transfer rates are received, the processing sequenceadvances to step S21 whereupon the NFC communication device performs thecommunication processing (communication processing of the initiator inthe passive mode) as the initiator in the passive mode. Here, thecommunication processing of the initiator in the passive mode will bedescribed later.

After ending the communication processing of the initiator in thepassive mode, the NFC communication device advances from step S21 tostep S22 whereupon the output of the electromagnetic wave starting instep S11 and then the processing ends.

Next, a description is given of the processing of the target in thepassive mode by the NFC communication device with reference to FIG. 15.

In the processing of the target in the passive mode, first, in step S31,the NFC communication device sets the variable n indicating the transferrate as the initial value, e.g., 1 and then the processing sequenceadvances to step S32. In step S32, the NFC communication devicedetermines whether or not another device serving as the initiator in thepassive mode sends the polling request frame by the n-th rate.

When it is determined in step S32 the initiator in the passive mode doesnot send the polling request frame, that is, another device near the NFCcommunication device does not communicate the data by the n-th rate andthe polling request frame is not sent by the n-th rate, the processingsequence advances to step S33 whereupon the NFC communication devicedetermines whether or not the variable n is equal to the maximum valueN. When it is determined in step S33 that the variable n is not equal tothe maximum value N, that is, when the variable n is less than themaximum value N, the processing sequence advances to step S34 whereuponthe NFC communication device increments the variable n by one. Then, theprocessing sequence returns to step S32 and the processing in steps S32to S34 is repeated.

When it is determined in step S33 that variable n is equal to themaximum value N, the processing sequence returns to step S31 and thenthe processing in steps S31 to S34 is repeated. Until receiving thepolling request frame sent by any of the N transfer rates from theinitiator in the passive mode, the processing in steps S31 to S34 isrepeated.

When it is determined in step S32 that the initiator in the passive modesends the polling request frame, that is, the NFC communication devicenormally receives the polling request frame by the n-th rate, theprocessing sequence advances to step S35 whereupon the NFC communicationdevice determines the transfer rate between the initiators as the n-thtransfer rate. Further, the NFC communication device generates the NFCIDthereof by the random number and then the processing sequence advancesto step S36. In step S36, the NFC communication device sends the pollingresponse frame having the NFCID thereof by the n-th rate and then theprocessing sequence advances to step S37.

After the NFC communication device sends the polling response frame bythe n-th rate in step S36, the NFC communication device communicates thedata by the n-th rate only when the initiator in the passive mode sendsthe command PSL_REQ to indicate the change of the transfer rate.

In step S37, the NFC communication device determines whether or not theinitiator in the passive mode sends the command DSL_REQ. When it isdetermined in step S37 that the command DSL_REQ is not sent, theprocessing sequence returns to step S37 whereupon the NFC communicationdevice waits for the transmission of the command DSL_REQ from theinitiator in the passive mode.

When it is determined in step S37 that the initiator in the passive modesends the command DSL_REQ, that is, the NFC communication devicereceives the command DSL_REQ, the processing sequence advances to stepS38 whereupon the NFC communication device sends the response DSL_REQfor the command DSL_REQ, thereby entering the deselecting state. Then,the processing sequence advances to step S39.

In step S39, the NFC communication device performs the communicationprocessing (communication processing of the target in the in the passivemode) as the target in the passive mode. The communication processing ofthe target in the passive mode ends and then the processing ends. Thecommunication processing of the target in the passive mode will bedescribed later.

Next, a description is given of the processing of the initiator in theactive mode by the NFC communication device with reference to aflowchart of FIG. 16.

In steps S51 to S61, the initiator in the active mode performs the sameprocessing in steps S11 to S21 as that of the initiator in the passivemode in FIG. 14. In the processing of the initiator in the passive modeshown in FIG. 14, the NFC communication device continuously outputs theelectromagnetic wave until the processing ends. In the processing of theinitiator in the active mode, unlike the initiator in the passive mode,the NFC communication device outputs the electromagnetic wave only whenthe data is sent.

That is, in step S51, the NFC communication device starts to output theelectromagnetic wave. The processing in step S51 in the processing ofthe initiator in the active mode is performed when the electromagneticwave is not detected in step S1 in FIG. 13. That is, when theelectromagnetic wave is not detected in step S1 in FIG. 13, in step S51,the NFC communication device starts to output the electromagnetic wave.Therefore, the processing in steps S1 and S51 corresponds to the initialRFCA processing.

After that, in step S52, the NFC communication device sets the variablen indicating the transfer rate as the initial value, e.g., one. Then,the processing advances to step S53. In step S53, the NFC communicationdevice sends the polling request frame by the n-th rate and stops theoutput of electromagnetic wave (hereinafter, properly referred to as RFoff-processing). The, the processing sequence advances to step S54.

In step S53, the NFC communication device starts to output theelectromagnetic wave by the active RFCA processing before sending thepolling request frame. However, when the variable n is one as theinitial value, the initial RFCA processing corresponding to theprocessing in steps S1 and S51 has already outputted the electromagneticwave. Therefore, the active RFCA processing is not necessary.

In step S54, the NFC communication device determines whether or notanother device sends the polling response frame by the n-th rate.

When it is determined that in step S54 that the other device does notsend the polling response frame, that is, when the other device near theNFC communication device does not communicate the data by the n-th rateand the polling response frame for the polling request frame sent by then-th rate is not returned, the processing in steps S55 to S57 is skippedand then the processing advances to step S58.

Further, when it is determined in step S54 that the other device sendsthe polling response frame by the n-th rate, that is, when the otherdevice near the NFC communication device communicates the data by then-th rate and the polling response frame for the polling request framesent by the n-th rate is returned, the processing sequence advances tostep S55 whereupon the NFC communication device sets the other devicethat returns the polling response frame as the target in the active modeand the NFCID of the target is recognized by the NFCID arranged to thepolling response frame. Further, the NFC communication device recognizesthat the target is communicable by the n-th rate.

When the NFC communication device recognizes, in step S55, the NFCID ofthe target in the active mode and that the target is communicable by then-th rate, the transfer rate between the targets is determined as then-th rate. The data is communicated with the target by the n-th rateexcept for when the command PSL_REQ changes the transfer rate.

In step S56, the NFC communication device starts to output theelectromagnetic wave by the active RFCA processing and sends the commandDSL_REQ to the target of the NFCID recognized in step S55 (target in theactive mode) by the n-th rate. Thus, the target enters the deselectingstate for sending no response for the subsequently-sent polling requestframe. After that, the NFC communication device performs the RFoff-processing and then the processing sequence advances from step S56to step S57.

In step S57, the NFC communication device receives the response DSL_RESreturned by the target set in the deselecting state by the commandDSL_REQ in response to the command DSL_REQ sent in step S56 and then theprocessing sequence advances to step S58.

In step S58, the NFC communication device sends the polling requestframe in step S53 by the n-th rate and then determines whether or not apredetermined time passes.

When it is determined in step S58 that the polling request frame in stepS53 is sent by the n-th rate and then a predetermined time does notpass, the processing sequence returns to step S53. Then, the processingin steps S53 to S58 is repeated.

When it is determined in step S58 that the polling request frame in stepS53 is sent by the n-th rate and then a predetermined time passes, theprocessing sequence advances to step S59 whereupon the NFC communicationdevice determines whether or not the variable n is equal to the maximumvalue N. When it is determined in step S59 that the variable n is notequal to the maximum value N, that is, when the variable n is less thanthe maximum value N, the processing sequence advances to step S60whereupon the NFC communication device increments the variable n by oneand then the processing sequence returns to step S53. Then, theprocessing in steps S53 to S60 is repeated.

By repeating the processing in steps S53 to S60, the NFC communicationdevice sends the polling request frame by the N transfer rates andreceives the polling response frames returned by the transfer rates.

When it is determined in step S59 that the variable n is equal to themaximum value N, that is, when the NFC communication device sends thepolling request frames by N N transfer rates and receives the pollingresponse frames returned by the transfer rates, the processing sequenceadvances to step S61 whereupon the NFC communication device performs thecommunication processing (communication processing of the initiator inthe active mode) as the initiator in the active mode. Then, theprocessing ends. The communication processing of the initiator in theactive mode will be described later.

Next, a description is given of the processing of the target in theactive mode by the NFC communication device with reference to FIG. 17.

In the processing of the target in the active mode, in steps S71 to S79,the same processing as the processing of the target in the passive modein steps S31 to S39 in FIG. 15 is performed. In the processing of thetarget in the passive mode in FIG. 15, the NFC communication devicemodulates the load of the electromagnetic wave outputted by theinitiator in the passive mode to send the data. However, unlike theprocessing of the target in the passive mode, in the processing of thetarget in the active mode, the NFC communication device outputs theelectromagnetic wave by itself and sends the data.

That is, in the processing of the target in the active mode, in stepsS71 to S75, the same processing as that in steps S31 to S35 in FIG. 15is performed.

After the processing in step S75, the processing sequence advances tostep S76 whereupon the NFC communication device starts to output theelectromagnetic wave by the active RFCA processing, and sends thepolling response frame having the NFCID thereof by the n-th rate. Instep S76, the NFC communication device performs the RF off-processingand then the processing sequence advances to step S77.

After sending the polling response frame by the n-th rate in step S76,the NFC communication device communicates the data by the n-th rateexcept for when the change of transfer rate is instructed by sending thecommand PSL_REQ from the initiator in the active mode.

In step S77, the NFC communication device determines whether or not theinitiator in the active mode sends the command DSL_REQ. When it isdetermined in step S77 that the initiator in the active mode does notsend the command DSL_REQ, the processing sequence returns to step S77.Then, the NFC communication device waits for the transmission of thecommand DSL_REQ from the initiator in the active mode.

When it is determined in step S77 that the initiator in the active modesends the command DSL_REQ, that is, when the NFC communication devicereceives the command DSL_REQ, the processing sequence advances to stepS78 whereupon the NFC communication device starts to output theelectromagnetic wave by the active RFCA processing and sends theresponse DSL_REQ for the command DSL_REQ. Further, in step S78, the NFCcommunication device performs the RF off-processing, thereby enteringthe deselecting state. Then, the processing sequence advances to stepS79.

In step S79, the NFC communication device performs the communicationprocessing (communication processing of the target in the active mode)as the target in the active mode. Then, after ending the communicationprocessing of the target in the active mode, the processing ends. Thecommunication processing of the target in the active mode will bedescribed later.

Next, a description is given of the communication processing of theinitiator in the passive mode in step S21 in FIG. 14 with reference toflowcharts of FIGS. 18 and 19.

In step S91, the NFC communication device serving as the initiator inthe passive mode selects the device for communication (hereinafter,properly referred to as a target device) from the targets that recognizethe NFCIDs in step S15 in FIG. 14, and the processing routine advancesto step S92. In step S92, the command WUP_REQ is sent to the targetdevice. Thus, the command DSL_REQ in step S16 in FIG. 14 is sent,thereby resetting the deselecting state of the target device(hereinafter, properly referred to as “wake up”).

Then, the NFC communication device waits for the transmission of theresponse WUP_RES for the command WUP_REQ of the target device. Theprocessing advances to step S93 from step S92. The response WUP_RES isreceived and then the processing sequence advances to step S94. In stepS94, the NFC communication device sends the command ATR_REQ to thetarget device. The NFC communication device waits for the transmissionof the response ATR_RES for the command ATR_REQ of the target device andthen the processing sequence advances to step S95 from step S94. In stepS95, the response ATR_RES is received.

Here, the NFC communication device and the target device receive andsend the command ATR_REQ having the property and the response ATR_RES asmentioned above. Thus, the NFC communication device and the targetdevice recognize the communicable transfer rate.

After that, the processing sequence advances to step S96 from step S95.The NFC communication device sends the command DSL_REQ to the targetdevice, thereby setting the target device in the deselecting state. TheNFC communication device waits for the transmission of the responseDSL_RES for the command DSL_REQ of the target device. Then, theprocessing sequence advances to step S97 from step S96. The responseDSL_RES is received and then the processing sequence advances to stepS98.

In step S98, the NFC communication device determines whether or not allthe targets that recognize the NFCIDs in step S15 in FIG. 14 areselected as the target devices in step S91. When the NFC communicationdevices determines in step S98 that the target that is not selected asthe target device exists, the processing sequence returns to step S91whereupon the NFC communication device newly selects, as the targetdevice, one of the targets that are not selected as the target devicesand then the similar processing is repeated.

When the NFC communication device determines in step S98 that all thetargets that recognize the NFCIDs in step S15 in FIG. 14 are selected asthe target devices in step S91, that is, when the NFC communicationdevice receives and sends the command ATR_REQ and the response ATR_RESto/from all the targets that recognize the NFCIDs and thus the targetsrecognize the communicable transfer rates of the targets and theprocessing sequence advances to step S99. In step S99, the NFCcommunication device selects the device for communication (targetdevice) from the targets to which the command ATR_REQ and the responseATR_RES are received and sent in steps S94 and S95. Then, the processingsequence advances to step S100.

In step S100, the NFC communication device sends the command WUP_REQ tothe target device. Thus, in step S96, the command DSL_REQ is sent,thereby waking up the target device in the deselecting state. The NFCcommunication device waits for the transmission of the response WUP_RESfor the command WUP_REQ of the target device. Then, the processingsequence advances to step S101 from step S100. In step S101, theresponse WUP_RES is received and then the processing sequence advancesto step S111 in FIG. 19.

In step S111, the NFC communication device determines whether or not thetransfer rate such as the communication parameter for communication withthe target device is changed.

The NFC communication device receives, from the target device, theresponse ATR_RES in step S95 in FIG. 18, and recognizes, based on theproperty arranged to the response ATR_RES, the communication parametercommunicable by the target device. When the NFC communication device cancommunicate the data with the target device by the transfer rate higherthan the current one, the NFC communication device determines in stepS111 that the communication parameter is changed to change the transferrate to be higher. Further, when the NFC communication device cancommunicate the data with the target device by a transfer rate lowerthan the current transfer rate and the current communication environmenthas the high noise level, the NFC communication device determines instep S111 that the communication parameter is changed to change thetransfer rate to be lower so as to reduce the transfer error. When thedata can be communicated between the NFC communication device and thetarget device by the transfer rate different from the current transferrate, the communication can continue by the current transfer rate.

When it is determined in step S111 that the communication parameter forcommunication with the target device is not changed, that is, when thecommunication continues between the NFC communication device and thetarget device by the communication parameter such as the currenttransfer rate, the processing in steps S112 to S114 is skipped and thenthe processing sequence advances to step S115.

When it is determined in step S111 that the communication parameter inthe communication with the target device is changed, the processingroutine advances to step S112 whereupon the NFC communication devicearranges the value of the communication parameter after changing to thecommand PSL_REQ and sends the value of the communication parameter tothe target device. The NFC communication device waits for thetransmission of the response PSL_RES for the command PSL_REQ to thetarget device. Then, the processing routine advances from step S112 toS113 whereupon the response PSL_RES is received and the processingroutine advances to step S114.

In step S114, the NFC communication device changes the communicationparameter such as the transfer rate in the communication with the targetdevice to the value of the communication parameter arranged to thecommand PSL_REQ sent in step S112. The NFC communication devicecommunicates the data with the target device with the target device inaccordance with the communication parameter such as the transfer rate ofthe value changed in step S114 only when the command PSL_REQ and theresponse PSL_RES are received and sent again.

By the reception and transmission (negotiation) of the command PSL_REQand the response PSL_RES, except for the transfer rate, e.g., theencoding system of the encoding unit 16 (decoding unit 14) in FIG. 4 andthe modulating system of the modulating unit 19 and the load modulationunit 20 (demodulating unit 13) are performed for changing.

After that, in step S115, the NFC communication device determineswhether or not the data to be received or sent to/from the target deviceexists. When it is determined in step S115 that the data to be receivedor sent to/from the target device does not exist, steps S116 and S117are skipped and then the processing sequence advances to step S118.

When it is determined in step S115 that the data to be received or sentto/from the target device exists, the processing sequence advances tostep S116 whereupon the NFC communication device sends the commandDEP_REQ to the target device. When it is determined in step S115 thatthe data to be received or sent to/from the target device exists, instep S116, further, the NFC communication device arranges the data tothe command DEP_REQ and sends the data.

The NFC communication device waits for the transmission of the responseDEP_RES for the command DEP_REQ of the target device and then theprocessing sequence advances from step S116 to step S117 whereupon theresponse DEP_RES is received. Then, the processing sequence advances tostep S118.

By receiving and sending the command DEP_REQ and the response DEP_RES asmentioned above, so-called real data is received and sent between theNFC communication device and the target device.

In step S118, the NFC communication device determines whether or not thecommunication partner is changed. When it is determined in step S118that the communication partner is not changed, that is, when the data tobe received or sent to/from the target device exists, the processingsequence returns to step S111 and then the similar processing isrepeated.

When it is determined in step S118 that the communication partner ischanged, that is, when the data for reception/transmission to/from thetarget device does not exist but the data for reception and transmissionto/from another communication partner exists, the processing sequenceadvances to step S119 whereupon the NFC communication device sends thecommand DSL_REQ or RLS_REQ to the target device. The NFC communicationdevice waits for the transmission of the response DSL_RES or RLS_RES forthe command DSL_REQ or RLS_REQ of the target device and then theprocessing sequence advances from step S119 to S120 whereupon theresponse DSL_RES or RLS_RES is received.

The NFC communication device sends the command DSL_REQ or RLS_REQ to thetarget device as mentioned above. Thus, the target as the target deviceis released from the communication target with the NFC communicationdevice as the initiator. The target released by the command DSL_REQ isin the communicable state with the initiator again by the commandWUP_UP. The target released by the command RLS_REQ is not in thecommunicable state with the initiator by receiving and sending thepolling request frame and the polling response frame to/from theinitiator.

The target is released from the communication target with the initiator,by sending the command DSL_REQ or RLS_REQ as mentioned above from theinitiator to the target and further by disabling the near fieldcommunication due to the excessively far distance between the initiatorand the target. In this case, similarly to the target released by thecommand RLS_REQ, the communicable state with the initiator between thetarget and the initiator is established by receiving and sending thepolling request frame and the polling response frame.

Hereinbelow, complete release denotes the release of the target which iscommunicable with the initiator by receiving and sending the pollingrequest frame and the polling response frame between the target and theinitiator. Further, temporary release denotes the release of the targetwhich is communicable with the initiator again only by receiving andsending the polling request frame and the polling response frame betweenthe target and the initiator.

After the processing in step S120, the processing sequence advances tostep S121 whereupon the NFC communication device determines whether ornot all the targets that recognize the NFCIDs in step S15 in FIG. 14 arecompletely released. When it is determined in step S121 that all thetargets that recognize the NFCIDs in step S15 in FIG. 14 are notcompletely released, the processing sequence returns to step S99 in FIG.18 whereupon the NFC communication device selects one new target devicefrom completely non-released, that is, the targets temporarily released.Hereinafter, the similar processing is repeated.

When it is determined in step S121 that all the targets which recognizethe NFCIDs are completely released, the processing ends.

In steps S116 and S117 in FIG. 19, the data is sent and received(exchanged) between the target and the initiator by receiving andsending the command DEP_REQ and the response DEP_RES. One transactionindicates the reception and transmission of the command DEL_REQ and theresponse DEP_RES. After the processing in steps S116 and S117, theprocessing sequence returns to step S114 via steps S118, S111, S112, andS113, thus changing the communication parameter. Therefore, thecommunication parameter such as the transfer rate on the communicationbetween the target and the initiator can be changed every transaction.

In steps S112 and S113, the command PSL_REQ and the response PSL_RES arereceived and sent between the initiator and the target. In step S114,the communication mode between the initiator and the target serving asone communication parameter can be changed. Therefore, the communicationmode between the target and the initiator can be changed everytransaction. This means that the communication mode between the targetand the initiator must not be changed for one transaction.

Next, a description is given of the communication processing of thetarget in the passive mode in step S38 in FIG. 15 with reference to aflowchart of FIG. 20.

In steps S37 and S38 in FIG. 15, the NFC communication device serving asthe target in the passive mode the command DSL_REQ and the responseDSL_RES to/from the initiator in the passive mode, thereby being in thedeselecting state.

In step S131, the NFC communication device determines whether or not theinitiator sends the command WUP_REQ. When it is determined in step S131that the initiator does not send the command WUP_REQ, the processingsequence returns to step S131 whereupon the deselecting state is kept.

When it is determined in step S131 that the initiator sends the commandWUP_REQ, that is, when the NFC communication device receives the commandWUP_REQ, the processing sequence advances to step S131 whereupon the NFCcommunication device sends the response WUP_RES for the command WUP_REQand is waken up. Then, the processing sequence advances to step S133.

In step S133, the NFC communication device determines the initiatorsends the command ATR_REQ. When it is determined in step S133 that theinitiator does not send the command ATR_REQ, step S134 is skipped andthen the processing sequence advances to step S135.

When it is determined in step S133 that the initiator sends the commandATR_REQ, that is, when the NFC communication device receives the commandATR_REQ, the processing sequence advances to step S135 whereupon the NFCcommunication device sends the response ATR_RES for the command ATR_REQand then the processing sequence advances to step S135.

In step S135, the NFC communication device determines whether or not theinitiator sends the command DSL_REQ. When it is determined in step S135that the initiator sends the command DSL_REQ, that is, when the NFCcommunication device receives the command DSL_REQ, the processingsequence advances to step S136 whereupon the NFC communication devicesends the response DSL_RES for the command DSL_REQ. Then, the processingsequence returns to step S131. Thus, the NFC communication device is inthe deselecting state.

When it is determined in step S135 that the initiator does not send thecommand DSL_REQ, the processing sequence advances to step S137 whereuponthe NFC communication device determines whether or not the initiatorsends the command PSL_REQ. When it is determined in step S137 that theinitiator does not sent the command PSL_REQ, steps S138 and S139 areskipped and then the processing sequence advances to step S140.

When it is determined in step S137 that the initiator sends the commandPSL_REQ, that is, when the NFC communication device receives the commandPSL_REQ, the processing sequence advances to step S138 whereupon the NFCcommunication device sends the response PSL_RES for the command PSL_REQ.Then, the processing sequence advances to step S139. In step S139, theNFC communication device changes the communication parameter inaccordance with the command PSL_REQ from the initiator. Then, theprocessing sequence advances to step S140.

In step S140, the NFC communication device determines whether or not theinitiator sends the command DEP_REQ. When it is determined in step S140that the initiator does not send the command DEP_REQ, step S141 isskipped and then the processing sequence advances to step S142.

When it is determined in step S140 that the initiator sends the commandDEP_REQ, that is, when the NFC communication device receives the commandDEP_REQ, the processing sequence advances to step S141 whereupon the NFCcommunication device sends the response DEP_RES for the command DEP_REQ.Then, the processing sequence advances to step S142.

In step S142, the NFC communication device determines whether or not theinitiator sends the command RSL_REQ. When it is determined in step S142that the initiator does not send the command RSL_REQ, the processingsequence returns to step S133 and the similar processing is repeated.

When it is determined in step S142 that the initiator sends the commandRSL_REQ, that is, when the NFC communication device receives the commandRSL_REQ, the processing sequence advances to step S143 whereupon the NFCcommunication device sends the response RSL_RES for the command RSL_REQ.Thus, the communication with the initiator completely ends and theprocessing ends.

Next, FIGS. 21 and 22 are flowcharts specifically showing thecommunication processing of the initiator in the active mode in step S61in FIG. 16.

In the communication processing of the initiator in the passive modedescribed with reference to FIGS. 18 and 19, the initiator continuouslyoutputs the electromagnetic wave. However, in the communicationprocessing of the initiator in the active mode in FIGS. 21 and 22,before sending the command, the initiator performs the active RFCAprocessing and thus the output of electromagnetic wave starts. Afterending the transmission of the command, the processing (off processing)for stopping the output of the electromagnetic wave is executed. Exceptfor this, the communication processing of the initiator in the activemode in steps S151 to S161 in FIG. 21 is similar to the processing insteps S171 to S181 in FIG. 22, steps in S91 to S101 in FIG. 18, andsteps S111 to S121 in FIG. 19. Thus, a description thereof is omitted.

FIG. 23 is a flowchart specifically showing the communication processingof the target in the active mode in step S79 in FIG. 17.

In the communication processing of the target in the passive modedescribed with reference to FIG. 20, the target modulates the load ofthe electromagnetic wave outputted by the initiator. However, in thecommunication processing in the active mode in FIG. 23, before sendingthe command, the target performs the active RFCA processing, therebystarting the output of electromagnetic wave. After ending thetransmission of the command, processing (off processing) for stoppingthe output of electromagnetic wave is performed. Except for this, thecommunication processing of the target in the active mode in steps S191to S203 in FIG. 23 is similar to the processing and in steps S131 toS143 in FIG. 20 and therefore a description thereof is omitted.

Next, a description is given of a solving method of the problem of thehidden terminal in the NFC communication device with reference to FIGS.24 to 26.

FIG. 24 shows a relationship between positions of three NFCcommunication devices 1, 2, and 3 and levels of the electromagneticwave, that is, the levels of the magnetic flux of the electromagneticwave.

Referring to FIG. 24, the NFC communication device 2 is apart from theNFC communication device 1 by a short distance L₁₂. The NFCcommunication device 3 is apart from the NFC communication device 2 by adistance L₂₃ longer than the distance L₁₂. The NFC communication devices1 and 3 are apart from each other by a distance (L₁₂+L₂₃).

The NFC communication devices 1 to 3 receive and send the data to thecommunication partners by the transformer connection of the coils as theantennas 11 shown in FIG. 4. The communication partner of the NFCcommunication device is not only the NFC communication device but alsothe conventional IC card. However, when the communication partner, suchas the conventional IC card, of the NFC communication device needs thepower supply, the NFC communication device receives and sends the dataand supplies the power by the transformer connection.

The power generated by the transformer connection of the coils is higheras the coils are close to each other, and is attenuated ininproportional to the third power of the distance between the coils.

The density of magnetic flux of the electromagnetic wave outputted bythe NFC communication device 1 is monotoneously reduced ininproportional to approximately the third power of the distance from theNFC communication device 1. The density of magnetic flux of theelectromagnetic wave outputted by the NFC communication device 1 isdivided into a carrier component M_(carr1) and a signal componentM_(sig1) serving as the amount of modulation of the sent data. As shownin FIG. 24, the carrier component M_(carr1) and the signal componentM_(sig1) of the carrier component are attenuated in inproportional toapproximately the third power of the distance from the NFC communicationdevice 1.

Similarly, the densities of magnetic fluxes of the electromagnetic wavesoutputted by the NFC communication devices 2 and 3 are attenuated ininproportional to approximately the third power of the distance from theNFC communication devices 2 and 3, respectively. Incidentally, referringto FIG. 24 (similarly to FIGS. 25 and 26 which will be described later),the density of magnetic flux of the electromagnetic wave outputted bythe NFC communication device 2 is not shown. In the density of magneticflux of the electromagnetic wave outputted by the NFC communicationdevice 3, only a carrier component M_(carr3) is shown and the signalcomponent is not shown.

The NFC communication devices 1 to 3 are designed so that the operationfor obtaining the data by the demodulating unit 13 shown in FIG. 4 needsthe carrier component that is equal to a magnetic-flux density TH2 ormore of the carrier at the operating limit, serving as a predeterminedthreshold.

For example, it is assumed that, for communication, the NFCcommunication device 1 is on the sending side and the NFC communicationdevice 2 is on the receiving side. Then, referring to FIG. 24, the NFCcommunication device 2 on the receiving side is apart from the NFCcommunication device 1 by the distance L₁₂ by which the carriercomponent M_(carr1) of the electromagnetic wave outputted by the NFCcommunication device 1 on the sending side matches the magnetic-fluxdensity TH2 of the carrier at the operating limit, and the NFCcommunication device 2 is the farthest from the NFC communication device1 for communication.

When the distance between the NFC communication devices 1 and 2 islonger than the distance L₁₂, the carrier component M_(carr1) of theelectromagnetic wave from the NFC communication device 1, which isreceived by the NFC communication device 2, is lower than themagnetic-flux density TH2 of the carrier at the operating limit.Therefore, the NFC communication device 2 cannot receive the data sentfrom the NFC communication device 1. In this case, the magnetic-fluxdensity TH2 of the carrier at the operating limit limits the distancefor communication between the NFC communication devices 1 and 2 to bethe distance L₁₂ or less.

In order to use the carrier component having the magnetic-flux densityTH2 or more of the carrier at the operating limit, serving as thethreshold in the case of obtaining the data by the demodulating unit 13(FIG. 4) in the NFC communication device 2, a first method and a secondmethod can be used. That is, according to the first method, thedemodulating unit 13 is operated only when the demodulating unit 13receives, via the antenna 11 and the receiving unit 12, the carriercomponent having the magnetic-flux density TH2 or more of the carrier atthe operating limit. Further, according to the second method, thedemodulating unit 13 is operated only when the detecting unit 23 detectsthe carrier component having the magnetic-flux density TH2 or more ofthe carrier at the operating limit. According to the second method, thethreshold setting unit 24 shown in FIG. 4 sets, as a threshold, themagnetic-flux density TH2 of the carrier at the operating limit. Thedetecting unit 23 detects the electromagnetic wave at the level of themagnetic-flux density TH2 or more of the carrier at the operating limit,serving as the threshold.

As mentioned above, the NFC communication devices 1 to 3 are designed toneed the carrier component at the level of the magnetic-flux density TH2or more of the carrier at the operating limit, serving as the threshold,so as to obtain the data by the demodulating unit 13. Further, the NFCcommunication devices 1 to 3 are designed to start the output of theelectromagnetic wave when the detecting unit 23 (FIG. 4) does not detectthe carrier component at the level of the magnetic-flux density TH1 ormore for determining the suppression of the output of carrier, servingas another threshold.

As described with reference to FIGS. 9 and 10, the electromagnetic waveis not detected around the NFC communication devices 1 to 3, the NFCcommunication devices 1 to 3 perform the RFCA processing for startingthe outputs of the electromagnetic waves. When the electromagnetic waveis not detected in the RFCA processing, the carrier component at thelevel of the magnetic-flux density TH1 or more for determining thesuppression of the output of carrier is not detected.

Referring to FIG. 24, the NFC communication device 1 is apart from theNFC communication device 3 that is not the communication partner by thedistance (L₁₂+L₂₃) when the carrier component M_(carr3) of theelectromagnetic wave outputted by the NFC communication device 3 is lessthan the magnetic-flux density TH1 for determining suppression of outputof carrier in the NFC communication device 1 (shortest distance betweenthe NFC communication devices 1 and 3, by which both the NFCcommunication devices 1 and 3 simultaneously output the electromagneticwaves). In this case, the output of the electromagnetic wave by the NFCcommunication device 1 is not prevented by the output of theelectromagnetic wave by the NFC communication device 3.

The NFC communication devices 1 and 3 are apart from each other by thedistance (L₁₂+L₂₃) when the carrier component M_(carr3) of theelectromagnetic wave outputted by the NFC communication device 3 is lessthan the magnetic-flux density TH1 for determining suppression of outputof carrier in the NFC communication device 1. Then, the carriercomponent M_(carr1) outputted by the NFC communication device 1 isattenuated to be less than the magnetic-flux density TH1 for determiningsuppression of output of carrier in the NFC communication device 3.Therefore, the output of the electromagnetic wave of the NFCcommunication device 3 is not prevented by the output of theelectromagnetic wave of the NFC communication device 1. Here, the levelsof the electromagnetic waves outputted by the communication devices 1 to3 are similar.

As mentioned above, referring to FIG. 24, both the NFC communicationdevice 1 in the communication with the NFC communication device 2 andthe NFC communication device 3 in the non-communication with the NFCcommunication device 2 can output the electromagnetic waves. The NFCcommunication device 2 is near the NFC communication device 3, ratherthan the NFC communication device 1. Further, the NFC communicationdevice 2 is near the NFC communication device 1, rather than the NFCcommunication device 3. The electromagnetic wave from the NFCcommunication device 3 is received at the level higher than that of theNFC communication device 1. The electromagnetic wave from the NFCcommunication device 1 is received at the level higher than that of theNFC communication device 3.

Now, the communication is established between the NFC communicationdevices 1 and 2. When the electromagnetic wave received by the NFCcommunication device 2 from the NFC communication device 1 is influencedfrom the electromagnetic wave received by the NFC communication device 2from the NFC communication device 3, the NFC communication device 2normally does not receive the data from the NFC communication device 1serving as the communication partner. The electromagnetic wave from theNFC communication device 3 prevents the communication between the NFCcommunication devices 1 and 2.

The magnetic-flux density TH2 of the carrier at the operating limit ishigher than the magnetic-flux density TH1 for determining thesuppression of the output of carrier. Thus, the signal componentM_(sig1) of the electromagnetic wave received by the NFC communicationdevice 2 from the NFC communication device 1 is set to a value that isnot influenced from the carrier component M_(carr3) of theelectromagnetic wave received by the NFC communication device 2 from theNFC communication device 3.

As mentioned above, when the distance between the NFC communicationdevices 1 and 3 is the distance (L₁₂+L₂₃) by which the carrier componentM_(carr3) outputted from the NFC communication device 3 is attenuated tobe less than the magnetic-flux density TH1 for determining thesuppression of the output of carrier in the communication device 1, theminimum level of the carrier component for obtaining the signalcomponent that is not influenced from the carrier component M_(carr3) ofthe NFC communication device 3 in the NFC communication device 2 is themagnetic-flux density TH2 of the carrier at the operating limit. Inorder to obtain the data from the NFC communication device 1 in the NFCcommunication device 2, the carrier component M_(carr1) of theelectromagnetic wave outputted by the NFC communication device 1 needsto have the magnetic-flux density TH2 or more of the carrier at theoperating limit. Thus, in the NFC communication device 2, the output ofthe electromagnetic wave by the NFC communication device 3 that is notthe communication partner, thereby preventing the normal reception ofthe data having the signal component M_(sig1) sent from the NFCcommunication device 1, that is, the problem of the hidden terminal issolved.

That is, referring to FIG. 24, irrespective of the output of theelectromagnetic wave of the NFC communication device 1, it is possibleto output the electromagnetic wave by the NFC communication device 3 atthe position where the carrier component M_(carr1) of theelectromagnetic wave from the NFC communication device 1 is less thanthe magnetic-flux density TH1 for determining the suppression of theoutput of carrier. That is, both the NFC communication devices 1 and 3simultaneously output the electromagnetic waves.

Referring to FIG. 24, the NFC communication device 2 receives thecarrier component M_(carr1) having the magnetic-flux density TH2 of thecarrier at the operating limit from the NFC communication device 1, andfurther receives the carrier component M_(carr3) lower than themagnetic-flux density TH2 of the carrier at the operating limit from theNFC communication device 3. In order to obtain the data sent fromanother device, the NFC communication device 2 needs the carriercomponent having the magnetic-flux density TH2 or more of the carrier atthe operating limit. Therefore, the NFC communication device 2 normallyreceives the data sent from the NFC communication device 1 but normallydoes not receive the data sent from the NFC communication device 3.Further, the NFC communication devices 1 and 3 are apart from each otherby the distance (L₁₂+L₂₃) by which the carrier component M_(carr3) ofthe electromagnetic wave outputted from the NFC communication device 3is attenuated to be at the level of the magnetic-flux density TH1 fordetermining the suppression of the output of carrier in the NFCcommunication device 1. Therefore, depending on the determination of themagnetic-flux density TH2 of the carrier at the operating limit, thecarrier component M_(carr3) received by the NFC communication device 2from the NFC communication device 3 does not influence on the signalcomponent M_(sig1) received by the NFC communication device 2 from theNFC communication device 1. Therefore, the NFC communication device 2normally receives the data sent from the NFC communication device,irrespective of the output of the electromagnetic wave by the NFCcommunication device 3.

FIG. 25 shows the level of the electromagnetic wave when an NFCcommunication device 2′ exists, in addition to the NFC communicationdevices 1 to 3 shown in FIG. 24.

The NFC communication device 2′ is near the NFC communication device 1,rather than the NFC communication device 2, and is far from the NFCcommunication device 3, rather than the NFC communication device 2.

Hereinbelow, a carrier component M_(carr#i(#j)) denotes a carriercomponent M_(carr#i) of the electromagnetic wave outputted by the NFCcommunication device #i, and a signal component M_(sig#i(#j)) denoteslevel (density of magnetic flux) of the NFC communication device #j ofthe signal component M_(sig#i).

Referring to FIG. 25, in the communication between the NFC communicationdevices 1 and 2′, the NFC communication device 2′ is near the NFCcommunication device 1, rather than the NFC communication device 2. Thecarrier component M_(carr1(2′)) received by the NFC communication device2′ from the NFC communication device 1 is higher than the carriercomponent M_(carr1(2)) received by the NFC communication device 2 fromthe NFC communication device 1. Therefore, the signal componentM_(sig1(2′)) received by the NFC communication device 2′ from the NFCcommunication device 1 is higher than the signal component M_(sig1(2))received by the NFC communication device 2 from the NFC communicationdevice 1.

The NFC communication device 2′ is apart from the NFC communicationdevice 3, rather than the NFC communication device 2. The carriercomponent M received by the NFC communication device 2′ from the NFCcommunication device 3 is lower than a carrier component M_(carr3(2))received by the NFC communication device 2 from the NFC communicationdevice 3.

In the communication between the NFC communication devices 1 and 2, aratio of the signal component M_(sig1(2)) received by the NFCcommunication device 2 from the NFC communication device 1 to thecarrier component M_(carr3(2)) received by the NFC communication device2 from the NFC communication device 3 becomes an S/N (Signal Noise)ratio. Similarly, in the communication between the NFC communicationdevices 1 and 2′, a ratio of the signal component M_(sig1(2′)) receivedby the NFC communication device 2′ from the NFC communication device 1to the carrier component M_(carr3(2′)) received by the NFC communicationdevice 2′ from the NFC communication device 3 becomes an S/N ratio.

As mentioned above, the signal component M_(sig1(2′)) received by theNFC communication device 2′ from the NFC communication device 1 ishigher than the signal component M_(sig1(2)) received by the NFCcommunication device 2 from the NFC communication device 1. The carriercomponent M_(carr3(2)) received by the NFC communication device 2′ fromthe NFC communication device 3 is lower than the carrier componentM_(carr3(2)) received by the NFC communication device 2 from the NFCcommunication device 3.

Therefore, the S/N ratio (≡M_(sig1(2′))/M_(carr3(2′))) of the NFCcommunication device 2′ is more preferable than the S/N ratio(≡M_(sig1(2))/M_(carr3(2))) of the NFC communication device 2.

As mentioned above, the NFC communication device 2′ serving as the NFCcommunication device is near the NFC communication device 1, rather thanthe NFC communication device 2, and is far from the NFC communicationdevice 3, rather than the NFC communication device 2. Then, the problemof the hidden terminal is solved.

When the NFC communication device 2′ is apart from the NFC communicationdevice 1 rather than the NFC communication device 2, the carriercomponent M_(carr1(2′)) received by the NFC communication device 2′ fromthe NFC communication device 1 is not equal to the magnetic-flux densityTH2 or more of the carrier at the operating limit. In this case, thecommunication between the communication devices 1 and 2′ is notestablished and therefore the problem of the hidden terminal is notcaused.

FIG. 26 shows the level of the electromagnetic wave when an NFCcommunication device 3′ exists in addition to the NFC communicationdevices 1 to 3 shown in FIG. 24.

The NFC communication device 3′ is apart from the NFC communicationdevices 1 and 2, rather than the NFC communication device 3.

The carrier component M_(carr1) of the electromagnetic wave outputted bythe NFC communication device 1 is attenuated to be at the level lowerthan the level of the magnetic-flux density TH1 for determining thesuppression of the output of carrier at the position of the NFCcommunication device 3′. The carrier component M_(carr3′) of theelectromagnetic wave outputted by the NFC communication device 3′ isattenuated the level lower than that of the magnetic-flux density TH1for determining the suppression of the output of carrier at the positionof the NFC communication device 1. Similarly to the case of the NFCcommunication devices 1 and 3 shown in FIG. 24, both the NFCcommunication devices 1 and 3′ simultaneously output the electromagneticwaves.

The NFC communication device 3′ is apart from the NFC communicationdevices 1 and 2, rather than the NFC communication device 3. The carriercomponent M_(carr3′(2)) received by the NFC communication device 2 fromthe NFC communication device 3′ is lower than the carrier componentM_(carr3(2)) received by the NFC communication device 2 from the NFCcommunication device 3.

In the communication of the NFC communication device 2 with the NFCcommunication device 1, the electromagnetic wave outputted by the NFCcommunication device 3 or 3′ is equal to the noises. As mentioned above,the carrier component M_(carr3′(2)) received by the NFC communicationdevice 2 from the NFC communication device 3′ is lower than the carriercomponent M_(carr3(2)) received by the NFC communication device 2 fromthe NFC communication device 3.

Therefore, in the case of the S/N ratio of the communication of the NFCcommunication device 2 with the NFC communication device 1, the S/Nratio (≡M_(sig1(2))/M_(carry3′(2))) in the case of outputting theelectric waves by the NFC communication device 3′ is more preferablethan the S/N ratio (≡M_(sig1(2))/M_(carr3(2))) in the case of outputtingthe NFC communication device 3.

As mentioned above, when the NFC communication device 3′ that is not thecommunication partner is apart from the NFC communication devices 1 and2 for communication rather than the NFC communication device 3, theproblem of the hidden terminal is solved.

When the NFC communication device 3′ is near the NFC communicationdevice 1, rather than the NFC communication device 3, the carriercomponent M_(carr1) of the electromagnetic wave outputted by the NFCcommunication device 1 reaches the NFC communication device 3′ at thelevel of the magnetic-flux density TH1 or more for determining thesuppression of the output of carrier. In this case, the NFCcommunication device 3′ does not output the electromagnetic wave andtherefore the problem of the hidden terminal is not caused.

In the above case, the NFC communication device 1 outputs theelectromagnetic wave so that the NFC communication device 2 sends thedata and the NFC communication device 2 receives the data. Further, whenthe NFC communication device 2 sends the data to the NFC communicationdevice 1 and the NFC communication device 1 receives the data, the NFCcommunication device 3 outputs the electromagnetic wave and thus it ispossible to prevent the data reception of the NFC communication device1, that is, the problem of the hidden terminal is solved.

When the NFC communication device 2 is the initiator in the passive modeor communicates the data in the active mode, the NFC communicationdevice 2 outputs the electromagnetic wave by itself and sends the data.When the NFC communication device 2 near the NFC communication device 3rather than the NFC determined device 1 outputs the electromagnetic waveto the NFC communication device 3, the NFC communication device 2reaches the NFC communication device 3 at the level of the carriercomponent of the electromagnetic wave higher than that of themagnetic-flux density TH1 for determining the suppression of output ofcarrier. The NFC communication device 3 does not output theelectromagnetic wave and the problem of the hidden terminal is notcaused.

When the NFC communication device 2 is the target in the passive mode,the NFC communication device 2 modulates the load of the electromagneticwave outputted by the NFC communication device 1 serving as theinitiator in the passive mode and sends the electromagnetic wave to theNFC communication device 1. When the signal component that reaches theNFC communication device 1 by the load modulation is influenced from theelectromagnetic wave outputted by the NFC communication device 3, theNFC communication device 1 does not receive the data sent from the NFCcommunication device 2.

On the contrary, when the NFC communication devices 1 and 3 are apartfrom each other by the distance (L₁₂+L₂₃) by which the carrier componentM_(carr3) of the electromagnetic wave outputted by the NFC communicationdevice 3 (1) is less than the magnetic-flux density TH1 for determiningthe suppression of the output of carrier, the data sent from the NFCcommunication device 2 is received by receiving, in the NFCcommunication device 1, the signal component as a result of the loadmodulation of the NFC communication device 2 which is not influencedfrom the carrier component M_(carr3) of the NFC communication device 3.

As mentioned above, the load modulation ratio of the load modulation ofthe NFC communication device 2 is set so as to set, to be sufficientlyhigher, the S/N ratio of the signal component that reaches to the NFCcommunication device 1 by the load modulation of the NFC communicationdevice 2 to the electromagnetic wave outputted by the NFC communicationdevice 3 by the load modulation. Then, when the NFC communicationdevices 1 and 3 are apart from each other by the distance (L₁₂+L₂₃) bywhich the carrier component M_(carr3) of the electromagnetic waveoutputted by the NFC communication device 3 (1) is less than themagnetic-flux density TH1 for determining the suppression of the outputof carrier, the carrier component M_(carr1) of the electromagnetic waveoutputted by the NFC communication device 1 in the NFC communicationdevice 2 is the magnetic-flux density TH2 of the carrier at theoperating limit to ensure the minimum S/N ratio to normally receive thedata from the NFC communication device 2 by the NFC communication device1 without any influence from the electromagnetic wave from the NFCcommunication device 3 and the problem of the hidden terminal is solved.

Next, a description is given of control processing (processing forcontrolling the reception and transmission) of the data when the problemof the hidden terminal is solved and the data is received and sent asmentioned above with reference to FIGS. 24 to 26. The processing forcontrolling the reception and the transmission is performed by thecontrol unit 21 shown in FIG. 4.

A description is given of the processing for controlling the receptionand transmission of the initiator in the passive mode when the NFCcommunication device becomes the initiator in the passive mode withreference to a flowchart of FIG. 27.

In step S211, the control unit 21 (FIG. 4) determines whether or not thedetecting unit 23 detects the electromagnetic wave at the level of themagnetic-flux density TH1 or more for determining the suppression of theoutput of carrier. When it is determined in step S211 that the detectingunit 23 detects the electromagnetic wave at the level of themagnetic-flux density TH1 or more for determining the suppression of theoutput of carrier, the processing sequence returns to step S211. Thatis, when the electromagnetic wave at the level of the magnetic-fluxdensity TH1 or more for determining the suppression of the output ofcarrier is detected, the electromagnetic wave is not outputted.Therefore, the determination as whether or not the electromagnetic waveat the level of the magnetic-flux density TH1 or more for determiningthe suppression of the output of carrier is detected is continued. Inthe processing in step S211, the threshold setting unit 24 sets thethreshold supplied to the detecting unit 23 to the magnetic-flux densityTH1 for determining the suppression of the output of carrier, andsupplies the set threshold to the detecting unit 23.

When it is determined in step S211 that the electromagnetic wave at thelevel of the magnetic-flux density TH1 or more for determining thesuppression of the output of carrier is not detected, the processingsequence advances to step S212 whereupon the control unit 21 permits theoutput of the electromagnetic wave by the electromagnetic-wave outputunit 18 and the data transmission by modulating the electromagneticwave. Then, the processing sequence advances to step S213. Thus, theelectromagnetic-wave output unit 18 starts to output the electromagneticwave and the modulating unit 19 enters a state for modulating theelectromagnetic wave. As mentioned above, the initiator in the passivemode continuously output the electromagnetic wave until thecommunication with the target ends.

In step S213, the control unit 21 allows the demodulating unit 13 of thereception and demodulation of the data sent by modulating the load ofthe electromagnetic wave outputted by itself by the target in thepassive mode, and the processing sequence advances to step S214. Thus,the demodulating unit 13 starts to demodulate the data sent bymodulating the load of the electromagnetic wave outputted by theinitiator in the passive mode by the target in the passive mode.

Then, the processing sequence advances to step S214 whereupon thecontrol unit 21 determines whether or not the communication with thetarget in the passive mode completely ends. When it is determined instep S214 that the communication with the target in the passive modecompletely does not end, the processing sequence returns to step S214.When it is determined in step S214 that, the control unit 21 prohibitsthe output of electromagnetic wave by the electromagnetic-wave outputunit 18, the data transmission by modulating the electromagnetic wave,and the data reception by the demodulating the electromagnetic waveload-modulated, and the processing ends.

Next, a description is given of the processing for controlling thereception and transmission of the target in the passive mode when theNFC communication device becomes the target in the passive mode withreference to a flowchart of FIG. 28.

In step S221, the control unit 21 (FIG. 4) determines whether or not thedetecting unit 23 detects the electromagnetic wave at the magnetic-fluxdensity TH2 or more of the carrier at the operating limit. In theprocessing in step S221, the threshold setting unit 24 sets thethreshold of the detecting unit 23 to the magnetic-flux density TH2 ofthe carrier at the operating limit, and supplies the threshold to thedetecting unit 23.

When it is determined in step S221 that the detecting unit 23 detectsthe electromagnetic wave at the magnetic-flux density TH2 or more of thecarrier at the operating limit, the processing sequence advances to stepS222 whereupon the control unit 21 permits the data reception bydemodulating the electromagnetic wave sent from the initiator in thepassive mode and the data transmission by modulating the load of theelectromagnetic wave, and the processing sequence advances to step S224.Thus, the load modulation unit 20 enters a state of modulating the loadof the electromagnetic wave. The demodulating unit 13 starts todemodulate the electromagnetic wave outputted by the initiator in thepassive mode.

When it is determined in step S221 that the detecting unit 23 does notdetect the electromagnetic wave at the magnetic-flux density TH2 or moreof the carrier at the operating limit, the processing sequence advancesto step S223 whereupon the control unit 21 prohibits the data receptionby demodulating the electromagnetic wave by the demodulating unit 13 andthe data transmission by modulating the electromagnetic wave by the loadmodulation unit 20 and then the processing sequence advances to S224.

In step S224, the control unit 21 determines whether or not thecommunication with the initiator in the passive mode completely ends.When it is determined in step S224 that the communication with theinitiator in the passive mode completely does not end, the processingsequence returns to step S221. When it is determined in step S221 thatthe communication with the initiator in the passive mode completelyends, the control unit 21 prohibits the data reception by demodulatingthe electromagnetic wave by the demodulating unit 13 and the datatransmission by modulating the load of the electromagnetic wave by theload modulation unit 20, and the processing sequence ends.

Next, a description is given of the processing for controlling thereception and transmission of the initiator in the active mode when theNFC communication device becomes the initiator in the active mode withreference to a flowchart of FIG. 29.

First, in step S231, the control unit 21 (FIG. 4) determines whether ornot the detecting unit 23 detects the electromagnetic wave at the levelof the magnetic-flux density TH1 or more for determining the suppressionof the output of carrier. In the processing in step S231, the thresholdsetting unit 24 sets the threshold supplied to the detecting unit 23 tothe magnetic-flux density TH1 for determining the suppression of theoutput of carrier, and supplies the threshold to the detecting unit 23.

When it is determined in step S231 that the detecting unit 23 detectsthe electromagnetic wave at the level of the magnetic-flux density TH1or more for determining the suppression of the output of carrier, theprocessing sequence advances to step S232, the control unit 21 prohibitsthe output of the electromagnetic wave by the electromagnetic-waveoutput unit 18 and the data transmission by modulating theelectromagnetic wave by the modulating unit 19. Then, the processingsequence advances to step S234. That is, when the electromagnetic waveis at the level of the magnetic-flux density TH1 or more for determiningthe suppression of the output of carrier, the electromagnetic wave isoutputted. Therefore, the output of the electromagnetic wave and thedata transmission of the electromagnetic wave are prohibited.

When it is determined in step S231 that the detecting unit 23 does notdetect the electromagnetic wave at the level of the magnetic-fluxdensity TH1 or more for determining the suppression of the output ofcarrier, the processing sequence advances to step S233 whereupon thecontrol unit 21 permits the output of the electromagnetic wave and thedata transmission by modulating the electromagnetic wave by theelectromagnetic-wave output unit 18 and then the processing sequenceadvances to step S234. Thus, the electromagnetic-wave output unit 18 canstart to output the electromagnetic wave and the modulating unit 19 canmodulate the electromagnetic wave.

In step S234, the control unit 21 determines whether or not thedetecting unit 23 detects the electromagnetic wave at the level of themagnetic-flux density TH2 or more of the carrier at the operating limit.In the processing in step S234, the threshold setting unit 24 sets thethreshold supplied to the detecting unit 23 to the magnetic-flux densityTH2 of the carrier at the operating limit, and supplies the threshold tothe detecting unit 23.

When it is determined in step S234 that the detecting unit 23 detectsthe electromagnetic wave at the level of the magnetic-flux density TH2or more of the carrier at the operating limit, the processing sequenceadvances to step S235 whereupon the control unit 21 permits the datareception by modulating the electromagnetic wave sent from the target inthe active mode and then the processing sequence advances to step S237.Thus, the demodulating unit 13 can demodulate the electromagnetic waveoutputted by the target in the active mode.

When it is determined in step S234 that the detecting unit 23 does notdetect the electromagnetic wave at the level of the magnetic-fluxdensity TH2 or more of the carrier at the operating limit, theprocessing sequence advances to step S236 whereupon the control unit 21prohibits the data reception by demodulating the electromagnetic wave bythe demodulating unit 13 and then the processing sequence advances tostep S237.

In step S237, the control unit 21 determines whether or not thecommunication with the target in the active mode completely ends. Whenit is determined in step S237 that the communication with the target inthe active mode completely does not end, the processing sequence returnsto step S231. When it is determined in step S237 that the communicationwith the target in the active mode completely ends, the control unit 21prohibits the output of the electromagnetic wave by theelectromagnetic-wave output unit 18, the data reception by demodulatingthe electromagnetic wave by the demodulating unit 13, and the datatransmission by modulating the electromagnetic wave by the modulatingunit 19 and then the processing sequence ends.

FIG. 30 shows a flowchart for describing the processing for controllingthe reception and the transmission of the target in the active mode whenthe NFC communication device becomes the target in the active mode. Theprocessing for controlling the reception and the transmission of thetarget in the active mode in steps S241 to S247 is the similar to thatin steps S231 to 237 in FIG. 29 and therefore a description thereof isomitted.

As mentioned above, when the electromagnetic wave at the level of themagnetic-flux density TH1 or more for determining the suppression of theoutput of carrier is not detected, the NFC communication device needsthe electromagnetic wave at the level of the magnetic-flux density TH1for determining the suppression of the output of carrier higher than themagnetic-flux density TH2 or more of the carrier at the operating limitso as to start the output of the electromagnetic wave and normallyreceive the data. The problem of the hidden terminal is easily solvedonly by detecting the electromagnetic wave.

That is, the NFC communication device does not need the control logicand memory that are used by the solving method of the problem of thehidden terminal using the commands RTS and CTS and therefore the problemof the hidden terminal is solved with low costs.

Further, the NFC communication device does not need the reception andthe transmission of the commands RTS and CTS and therefore the problemof the hidden terminal is fast solved.

In addition, the NFC communication device needs the electromagnetic waveat the level of magnetic-flux density TH2 or more of the carrier at theoperating limit, higher than the magnetic-flux density TH1 fordetermining suppression of output of carrier, so as to normally receivethe data. Thus, the distance for receiving and sending the data to/fromthe communication partner is limited within a predetermined distance.Further, the antenna 11 is used as the coil and the wirelesscommunication path by the transformer combination is established. Thedistance between the NFC communication devices is longer and thus theattenuation of the electromagnetic wave is increased. The restriction ofthe distance to the communication partner to normally receive the datais strict (necessarily kept).

When the detecting unit 23 does not detect the electromagnetic wave atthe level of the magnetic-flux density TH2 or more of the carrier at theoperating limit, the data reception is prevented by prohibiting the datademodulation of the demodulating unit 13. In addition, when the NFCcommunication device needs the power supply from the communicationpartner like the conventional IC card, the power necessary for thedevice operation is obtained by receiving the electromagnetic wave atthe level of the magnetic-flux density TH2 or more of the carrier at theoperating limit. Thus, the data reception needs the electromagnetic waveat the magnetic-flux density TH2 or more of the carrier at the operatinglimit.

In the above case, the threshold setting unit 24 sets, as the threshold,the magnetic-flux density TH1 for determining suppression of output ofcarrier or the magnetic-flux density TH2 of the carrier at the operatinglimit, and the detecting unit 23 detects the electromagnetic wave at thelevel of the magnetic-flux density TH1 or more for determining thesuppression of the output of carrier and at the level of themagnetic-flux density TH2 or more of the carrier at the operating limit.As described with reference to FIG. 4, the detecting units 23 and 25individually detect the electromagnetic waves at the levels of themagnetic-flux density TH1 or more for determining the suppression of theoutput of carrier and of the magnetic-flux density TH2 or more of thecarrier at the operating limit. However, it is more advantageous in viewof costs to detect, only by the detecting unit 23, the electromagneticwaves at the levels of the magnetic-flux density TH1 or more fordetermining the suppression of the output of carrier and of themagnetic-flux density TH2 or more of the carrier at the operating limit,as compared with the case of arranging the detecting units 23 and 25.

In the description, the processing steps of the NFC communication deviceare not in accordance with the sequence described in the flowchart. Theparallel or individual processing (e.g., parallel processing or objectprocessing) is included.

According to the embodiments of the present invention, the NFCcommunication device can receive and send the data by a plurality oftransfer rates. Further, according to the present invention, thecommunication device receives and sends the data only by one transferrate.

INDUSTRIAL APPLICABILITY

According to the present invention, the problem of the hidden terminalis easily solved.

1. A method for a communication device, comprising: determining whethera first radio frequency (RF) signal at a level of at least a firstpredetermined field threshold is detected; generating a second RF signalat a level of at least a second predetermined field threshold greaterthan the first predetermined field threshold, when the communicationdevice receives an instruction to generate the second RF signal and thedetermining determines that the first RF signal at the level of at leastthe first predetermined field threshold is not detected; and receiving aload modulated RF signal in response to the second RF signal.
 2. Themethod according to claim 1, further comprising: preventing a generationof the second RF signal, when the communication device receives theinstruction to generate the second RF signal and the determiningdetermines that the first RF signal at the level of at least the firstpredetermined field threshold is detected.
 3. The method according toclaim 1, wherein the determining determines whether the first RF signalat the level of at least the first predetermined field threshold wasdetected during a duration ofT _(IDT) +n×T _(RFW), where T_(IDT)>4096/fc, T_(RFW)=512/fc, and 0≦n≦3,fc being a carrier frequency of the second RF signal, n being a randomlygenerated number.
 4. The method according to claim 1, wherein a carrierfrequency of the first RF signal is 13.56 MHz, and a carrier frequencyof the second RF signal is 13.56 MHz.
 5. A communication device,comprising: a control unit that determines whether a first radiofrequency (RF) signal at a level of at least a first predetermined fieldthreshold is detected; an output unit that generates a second RF signalat a level of at least a second predetermined field threshold greaterthan the first predetermined field threshold, when the communicationdevice receives an instruction to generate the second RF signal and thecontrol unit determines that the first RF signal at the level of atleast the first predetermined field threshold is not detected; and areceiving unit that receives a load modulated RF signal in response tothe second RF signal.
 6. The communication device according to claim 5,wherein the control unit is configured to prevent a generation of thesecond RF signal, when the communication device receives the instructionto generate the second RF signal and the control unit determines thatthe first RF signal at the level of at least the first predeterminedfield threshold is detected.
 7. The communication device according toclaim 5, wherein the control unit is configured to determine whether thefirst RF signal at the level of at least the first predetermined fieldthreshold was detected during a duration ofT _(IDT) +n×T _(RFW), where T_(IDT)>4096/fc, T_(RFW)=512/fc, and 0≦n≦3,fc being a carrier frequency of the second RF signal, n being a randomlygenerated number.
 8. The communication device according to claim 5,wherein a carrier frequency of the first RF signal is 13.56 MHz, and acarrier frequency of the second RF signal is 13.56 MHz.
 9. Acommunication device, comprising: means for determining whether a firstradio frequency (RF) signal at a level of at least a first predeterminedfield threshold is detected; means for generating a second RF signal ata level of at least a second predetermined field threshold greater thanthe first predetermined field threshold, when the communication devicereceives an instruction to generate the second RF signal and the meansfor determining determines that the first RF signal at the level of atleast the first predetermined field threshold is not detected; and meansfor receiving a load modulated RF signal in response to the second RFsignal.
 10. The communication device according to claim 9, wherein themeans for determining prevents a generation of the second RF signal,when the communication device receives the instruction to generate thesecond RF signal and the means for determining determines that the firstRF signal at the level of at least the first predetermined fieldthreshold is detected.
 11. The communication device according to claim9, wherein the means for determining determines whether the first RFsignal at the level of at least the first predetermined field thresholdwas detected during a duration ofT _(IDT) +n×T _(RFW), where T_(IDT)>4096/fc, T_(RFW)=512/fc, and 0≦n≦3,fc being a carrier frequency of the second RF signal, n being a randomlygenerated number.
 12. The communication device according to claim 9,wherein a carrier frequency of the first RF signal is 13.56 MHz, and acarrier frequency of the second RF signal is 13.56 MHz.